1
 
     INFORMATION CONTAINED HEREIN IS SUBJECT TO COMPLETION OR AMENDMENT. THIS
     PROSPECTUS SUPPLEMENT AND THE ACCOMPANYING PROSPECTUS SHALL NOT CONSTITUTE
     AN OFFER TO SELL OR THE SOLICITATION OF AN OFFER TO BUY NOR SHALL THERE BE
     ANY SALE OF THESE SECURITIES IN ANY STATE IN WHICH SUCH OFFER, SOLICITATION
     OR SALE WOULD BE UNLAWFUL PRIOR TO REGISTRATION OR QUALIFICATION UNDER THE
     SECURITIES LAWS OF ANY SUCH STATE.
 
                SUBJECT TO COMPLETION, DATED SEPTEMBER 23, 1994
          PROSPECTUS SUPPLEMENT TO PROSPECTUS DATED SEPTEMBER 13, 1994
 
                         3,880,000 PREFERRED SECURITIES
                             ILLINOIS POWER CAPITAL
      % CUMULATIVE MONTHLY INCOME PREFERRED SECURITIES ("MIPS"*), SERIES A
              (LIQUIDATION PREFERENCE $25 PER PREFERRED SECURITY)
                GUARANTEED TO THE EXTENT ILLINOIS POWER CAPITAL
                        HAS FUNDS AS SET FORTH HEREIN BY
                             ILLINOIS POWER COMPANY
                         ------------------------------
 
    The     % Cumulative Monthly Income Preferred Securities, Series A (the
"Series A Preferred Securities"), representing the limited partner interests
offered hereby, are being issued by Illinois Power Capital, L.P., a limited
partnership formed under the laws of the State of Delaware ("Illinois Power
Capital"). All of the general partner interests in Illinois Power Capital are
owned by Illinois Power Company, an Illinois corporation (the "Company").
Illinois Power Capital exists for the sole purpose of issuing its partner
interests and using the proceeds thereof to purchase certain debt securities of
the Company. The proceeds of the Series A Preferred Securities will be used by
Illinois Power Capital to purchase the Company's   % Subordinated Deferrable
Interest Debentures, Series A (the "Series A Subordinated Debentures"). The
limited partner interests represented by the Series A Preferred Securities will
have a preference with respect to cash distributions and amounts payable on
liquidation over the general partner interests in Illinois Power Capital.
 
    Holders of the Series A Preferred Securities will be entitled to receive
cumulative preferential cash distributions at an annual rate of     % of the
liquidation preference of $25 per Series A Preferred Security, accruing from the
date of original issuance and payable monthly in arrears on the last day of each
calendar month of each year, commencing         , 1994 ("dividends"). The
payment of dividends and payments on liquidation of Illinois Power Capital or
the redemption of Series A Preferred Securities, to the extent that Illinois
Power Capital has sufficient cash on hand to permit such payments and funds
legally available therefor, are guaranteed by the Company to the extent set
forth herein and in the accompanying Prospectus (the "Guarantee"). See
"Description of the Guarantee" in the accompanying Prospectus. If the Company
fails to make interest payments on the Series A Subordinated Debentures
purchased by Illinois Power Capital with the proceeds of this offering, Illinois
Power Capital will have insufficient funds to pay dividends on the Series A
Preferred Securities. The Guarantee does not provide for payment by the Company
directly of dividends for which Illinois Power Capital does not have sufficient
funds available. In such event, the remedy of a holder of Series A Preferred
Securities is to enforce Illinois Power Capital's rights under the Series A
Subordinated Debentures purchased by Illinois Power Capital from the Company.
 
    The obligations of the Company under the Guarantee are subordinate and
junior in right of payment to all liabilities of the Company, and the Company's
obligations under the Series A Subordinated Debentures are subordinate and
junior in right of payment to all present and future Senior Indebtedness (as
defined in the accompanying Prospectus) of the Company. At June 30, 1994, Senior
Indebtedness of the Company aggregated approximately $2.2 billion.
                                                   (Continued on following page)
 
    SEE "CERTAIN INVESTMENT CONSIDERATIONS" FOR CERTAIN CONSIDERATIONS RELEVANT
TO AN INVESTMENT IN THE SERIES A PREFERRED SECURITIES, INCLUDING THE PERIOD
DURING WHICH AND CIRCUMSTANCES UNDER WHICH PAYMENT OF DIVIDENDS ON THE SERIES A
PREFERRED SECURITIES MAY BE DEFERRED.
 
    Application has been made to list the Series A Preferred Securities on the
New York Stock Exchange.
                         ------------------------------
 
THESE SECURITIES HAVE NOT BEEN APPROVED OR DISAPPROVED BY THE SECURITIES AND
EXCHANGE COMMISSION OR ANY STATE SECURITIES COMMISSION NOR HAS THE SECURITIES
  AND EXCHANGE COMMISSION OR ANY STATE SECURITIES COMMISSION PASSED UPON THE
    ACCURACY OR ADEQUACY OF THIS PROSPECTUS SUPPLEMENT OR THE PROSPECTUS TO
     WHICH IT RELATES.               ANY REPRESENTATION TO THE CONTRARY
       IS A CRIMINAL OFFENSE.


                                                                    INITIAL PUBLIC    UNDERWRITING     PROCEEDS TO ILLINOIS POWER
                                                                    OFFERING PRICE    COMMISSION(1)          CAPITAL(2)(3)
                                                                    --------------    -------------    --------------------------
                                                                                              
Per Series A Preferred Security..................................      $                   (2)                  $
Total............................................................      $                   (2)                  $

 
- ------------------
 
(1) Illinois Power Capital and the Company have agreed to indemnify the several
    Underwriters against certain civil liabilities, including liabilities under
    the Securities Act of 1933, as amended. See "Underwriting."
 
(2) As the proceeds of the sale of the Series A Preferred Securities will be
    loaned to the Company, the Company has agreed in the Underwriting Agreement
    to pay to the Underwriters $    per Series A Preferred Security (or $    in
    the aggregate); provided that such payment will be $
    per Series A Preferred Security sold to certain institutions. Therefore, to
    the extent that Series A Preferred Securities are sold to such institutions,
    the actual amount of Underwriters' compensation will be less than the amount
    specified in the preceding sentence and the Proceeds to Illinois Power
    Capital will be greater than the amount set forth in the table above. See
    "Underwriting."
 
(3) Expenses of the offering which are payable by the Company are estimated to
    be $350,000.
                         ------------------------------
 
    The Series A Preferred Securities offered hereby are offered severally by
the Underwriters, as specified herein, subject to receipt and acceptance by them
and subject to their right to reject any order in whole or in part. It is
expected that delivery of certificates for the Series A Preferred Securities
will be made only in book-entry form through the facilities of The Depository
Trust Company on or about         , 1994.
- ------------------
    * An application has been filed by Goldman, Sachs & Co. with the United
      States Patent and Trademark Office for the registration of the MIPS
      servicemark.
 
GOLDMAN, SACHS & CO.
         BEAR, STEARNS & CO. INC.
                         DEAN WITTER REYNOLDS INC.
                                   A.G. EDWARDS & SONS, INC.
                                PAINEWEBBER INCORPORATED
                                                    SALOMON BROTHERS INC
           The date of this Prospectus Supplement is         , 1994.
   2
 
     The Series A Preferred Securities are redeemable at the option of Illinois
Power Capital, in whole or in part, from time to time, on or after           ,
1999, at $25 per Series A Preferred Security plus any accumulated and unpaid
dividends thereon to the date fixed for redemption (the "Redemption Price"), and
will be redeemed at such price from the proceeds of any repayment or redemption
of the Series A Subordinated Debentures. See "Description of Series A Preferred
Securities -- Optional Redemption" and "-- Mandatory Redemption." In addition,
upon the occurrence of certain special events arising from a change in law or a
change in legal interpretation, the Series A Preferred Securities are redeemable
in whole at the Redemption Price at the option of the Company, in its capacity
as the general partner of Illinois Power Capital (the "General Partner"), or the
General Partner may dissolve Illinois Power Capital and cause Series A
Subordinated Debentures to be distributed to the holders of the Series A
Preferred Securities in liquidation of their interests in Illinois Power
Capital. See "Description of Series A Preferred Securities -- Special Event
Redemption or Distribution" and "Description of the Series A Subordinated
Debentures." If the Series A Subordinated Debentures are so distributed, the
Company will use its best efforts to have them listed on the same exchange on
which the Series A Preferred Securities are then listed.
 
     In the event of the dissolution of Illinois Power Capital, the holders of
Series A Preferred Securities will be entitled to a liquidation preference for
each Series A Preferred Security of $25 plus any accumulated and unpaid
dividends thereon to the date of payment, subject to certain limitations,
unless, in connection with such dissolution, Series A Subordinated Debentures
are distributed to the holders of the Series A Preferred Securities. See
"Description of Series A Preferred Securities -- Liquidation Distribution Upon
Dissolution."
                          ----------------------------
 
     IN CONNECTION WITH THIS OFFERING, THE UNDERWRITERS MAY OVER-ALLOT OR EFFECT
TRANSACTIONS WHICH STABILIZE OR MAINTAIN THE MARKET PRICE OF THE SECURITIES
OFFERED HEREBY AT LEVELS ABOVE THOSE WHICH MIGHT OTHERWISE PREVAIL IN THE OPEN
MARKET. SUCH TRANSACTIONS MAY BE EFFECTED ON THE NEW YORK STOCK EXCHANGE, IN THE
OVER-THE-COUNTER MARKET OR OTHERWISE. SUCH STABILIZING, IF COMMENCED, MAY BE
DISCONTINUED AT ANY TIME.
 
                                       S-2
   3
 
                       CERTAIN INVESTMENT CONSIDERATIONS
 
     Prospective purchasers of Series A Preferred Securities should carefully
review the information contained elsewhere in this Prospectus Supplement and in
the accompanying Prospectus and should particularly consider the following
matters. Capitalized terms used and not otherwise defined in this Prospectus
Supplement shall have the meanings ascribed thereto in the accompanying
Prospectus.
 
     SUBORDINATION OF GUARANTEE AND SERIES A SUBORDINATED DEBENTURES. The
Company's obligations under the Guarantee are subordinate and junior in right of
payment to all other liabilities of the Company. The obligations of the Company
under the Series A Subordinated Debentures are subordinate and junior in right
of payment to all present and future Senior Indebtedness of the Company. At June
30, 1994, Senior Indebtedness of the Company aggregated approximately $2.2
billion. There are no terms in the Series A Preferred Securities, the Series A
Subordinated Debentures or the Guarantee that limit the Company's ability to
incur additional indebtedness, including indebtedness that ranks senior to the
Series A Subordinated Debentures and the Guarantee. See "Description of the
Guarantee -- Status of the Guarantee" and "Description of the Subordinated
Debentures -- Subordination" in the accompanying Prospectus.
 
     OPTION TO EXTEND INTEREST PAYMENT PERIOD. The Company has the right under
the Indenture to extend the interest payment period from time to time on the
Series A Subordinated Debentures to a period not exceeding 60 consecutive
months, and, as a consequence, monthly dividends on the Series A Preferred
Securities would be deferred (but would continue to accrue with interest
thereon) by Illinois Power Capital during any such extended interest payment
period. In the event that the Company exercises this right, the Company may not
declare or pay dividends on, or redeem, purchase or acquire, any of its capital
stock until the deferred interest on the Series A Subordinated Debentures is
paid in full. Prior to the termination of any such extension period, the Company
may further extend the interest payment period, provided that such extension
period together with all such previous and further extensions thereof may not
exceed 60 consecutive months. Upon the termination of any extension period and
the payment of all amounts then due, the Company may select a new extension
period, subject to the above requirements. The Company has no current intention
of extending the interest payment period on the Series A Subordinated Debentures
since it desires to continue the declaration and payment of dividends on its
capital stock. See "Description of the Series A Preferred Securities --
Dividends" and "Description of the Series A Subordinated Debentures -- Option to
Extend Interest Payment Period."
 
     Should an extended interest payment period occur, Illinois Power Capital
will continue to accrue income for United States federal income tax purposes
which will be allocated, but not distributed, to holders of record of Series A
Preferred Securities. As a result, such a holder will include such interest in
gross income for United States federal income tax purposes in advance of the
receipt of cash, and will not receive the cash from Illinois Power Capital
related to such income if such a holder disposes of his or her Series A
Preferred Securities prior to the record date for payment of dividends. See
"United States Taxation -- Potential Extension of Interest Payment Period."
 
     SPECIAL EVENT REDEMPTION OR DISTRIBUTION. Upon the occurrence of a Special
Event (as defined herein), the General Partner will elect to either (i) redeem
the Series A Preferred Securities in whole or (ii) dissolve Illinois Power
Capital and cause Series A Subordinated Debentures to be distributed to the
holders of the Series A Preferred Securities in liquidation of their interests
in Illinois Power Capital. The Series A Subordinated Debentures will initially
be issued at face value as a Global Security (as defined herein) and will be
limited in aggregate principal amount to approximately $100 million, such amount
being the sum of the aggregate liquidation preference of the Series A Preferred
Securities and the General Partnership Payment (as defined herein). In the case
of a Tax Event (as defined herein), the General Partner may also elect to cause
the Series A Preferred Securities to remain outstanding. See "Description of the
Series A Preferred Securities -- Special Event Redemption or Distribution" and
"Description of the Series A Subordinated Debentures -- General."
 
     Under current United States federal income tax law, the distribution of
Series A Subordinated Debentures in connection with the dissolution of Illinois
Power Capital would not be a taxable event to
 
                                       S-3
   4
 
holders of the Series A Preferred Securities. Under a change in law, a change in
legal interpretation or the other circumstances giving rise to a Special Event,
however, the dissolution of Illinois Power Capital and the distribution of
Series A Subordinated Debentures in connection with the dissolution of Illinois
Power Capital could be a taxable event to holders of the Series A Preferred
Securities. In the judgment of tax counsel to the Company and Illinois Power
Capital, the series of events which would result in the recognition of taxable
gain by holders of the Series A Preferred Securities, by reason of a dissolution
of Illinois Power Capital in response to a Special Event, is unlikely to occur.
There can be no assurance in this regard, however. See "United States Taxation
- -- Receipt of Series A Subordinated Debentures Upon Dissolution of Illinois
Power Capital."
 
                             ILLINOIS POWER COMPANY
 
     The Company was incorporated under the laws of the State of Illinois on May
25, 1923. Effective May 27, 1994, the Company became a subsidiary of Illinova
Corporation, an exempt holding company under the Public Utility Holding Company
Act of 1935, as amended, pursuant to a merger in which each outstanding share of
the Company's Common Stock was converted into one share of common stock of
Illinova Corporation. The Company is engaged in the generation, transmission,
distribution and sale of electric energy and the distribution and sale of
natural gas in the State of Illinois. Its service area is a widely diversified
industrial and agricultural area comprising approximately 15,000 square miles in
northern, central and southern Illinois. Electric service is provided at retail
to 309 incorporated municipalities, adjacent suburban and rural areas and
numerous unincorporated municipalities having an aggregate population of
approximately 1,283,000. Gas service is provided to 257 incorporated
municipalities, adjacent suburban areas and numerous unincorporated
municipalities having an aggregate population of approximately 935,000. The
larger cities served include Decatur, East St. Louis (gas only), Champaign,
Danville, Belleville, Granite City, Bloomington (electric only), Galesburg,
Urbana and Normal (electric only). The executive offices of the Company are
located at 500 South 27th Street, Decatur, Illinois 62525, and the Company's
telephone number is (217) 424-6600.
 
                             ILLINOIS POWER CAPITAL
 
     Illinois Power Capital is a limited partnership formed under the Delaware
Revised Uniform Limited Partnership Act, as amended (the "Partnership Act").
Illinois Power Capital exists for the sole purpose of issuing its partner
interests, including the Series A Preferred Securities, and using the proceeds
thereof to purchase certain debt securities of the Company, including the Series
A Subordinated Debentures. The Company is the sole general partner (the "General
Partner") of Illinois Power Capital and will manage all of the business and
affairs of Illinois Power Capital. Holders of Series A Preferred Securities will
be limited partners of Illinois Power Capital. The Company, as the General
Partner of Illinois Power Capital, will make capital contributions to Illinois
Power Capital from time to time to the extent required so that the total
contributions made by the General Partner shall at all times be at least equal
to 3% of the total contributions made by all partners. The rights and
obligations of the General Partner and the limited partners of Illinois Power
Capital will be governed by the Partnership Act and by an Amended and Restated
Agreement of Limited Partnership of Illinois Power Capital (the "Partnership
Agreement") substantially in the form filed as an exhibit to the Registration
Statement of which this Prospectus Supplement and the accompanying Prospectus
form a part.
 
                                USE OF PROCEEDS
 
     The proceeds to be received by Illinois Power Capital from the sale of the
Series A Preferred Securities will be used to purchase Series A Subordinated
Debentures of the Company and will be applied by the Company to the payment or
provision for payment at maturity, or the purchase or the redemption prior to
maturity of outstanding securities of the Company, and for general corporate
purposes.
 
                                       S-4
   5
 
                  SUMMARY FINANCIAL INFORMATION OF THE COMPANY
                (THOUSANDS EXCEPT PER SHARE AMOUNTS AND RATIOS)
 


                                                                                               12 MONTHS
                                             YEAR ENDED DECEMBER 31,                             ENDED
                          --------------------------------------------------------------     JUNE 30, 1994
                             1989         1990         1991         1992       1993(A)     (UNAUDITED)(A)(B)
                          ----------   ----------   ----------   ----------   ----------   -----------------
                                                                         
INCOME STATEMENT DATA:
  Operating Revenues..... $1,393,778   $1,469,480   $1,474,905   $1,479,449   $1,581,190      $ 1,628,094
  Net Income.............   (288,432)     (78,484)     109,244      122,088      (56,038)         (42,031)
  Preferred Dividend
    Requirements.........     37,365       36,839       30,866       28,854       26,123           24,283
  Net Income Applicable
    to Common Stock......   (325,797)    (115,323)      78,378       93,234      (82,161)         (66,314)
  Earnings Per Share of
    Common Stock.........      (4.34)       (1.53)        1.04         1.23        (1.08)           (0.91)
  Ratio of Earnings to
    Fixed Charges(c).....      (0.52)(d)     0.70(d)      1.85         2.02         0.80(d)          0.93(d)
  Ratio of Earnings to
    Combined Fixed
    Charges and Preferred
    Stock Dividend
    Requirements(c)......      (0.45)(e)     0.60(e)      1.48         1.61         0.70(e)          0.82(e)

 


                                                                                   AMOUNT     PERCENTAGE
                                                                                 ----------   ----------
                                                                                        
CAPITALIZATION AT JUNE 30, 1994:
  Long-Term Debt...............................................................  $1,868,191       52.2%
  Preferred Stock (not subject to mandatory redemption)........................     303,705        8.5
  Preferred Stock (subject to mandatory redemption)............................      36,000        1.0
  Common Stock Equity..........................................................   1,368,858       38.3
                                                                                 ----------   ----------
      Total Capitalization.....................................................  $3,576,754      100.0%
                                                                                  =========   =========

 
- ---------------
(a) Subsequent to the Company's merger with Illinova Corporation, net assets of
    Illinova Generating Company (formerly IP Group, Inc.) were transferred in
    the form of a dividend from the Company to Illinova Corporation. The income
    statement data contained herein has been restated to reflect the financial
    results of the Company's current operations.
 
(b) In the opinion of the Company, all adjustments, consisting only of normal
    recurring adjustments, necessary for a fair statement of the results for the
    unaudited twelve-month period ended June 30, 1994, have been made.
 
(c) Earnings used in the calculation of the ratio of earnings to fixed charges
    and the ratio of earnings to combined fixed charges and preferred stock
    dividend requirements include the allowance for funds used during
    construction and the deferred financing costs associated with the Company's
    Clinton Power Station, and are before deduction of income taxes and fixed
    charges. Fixed charges include interest on long-term debt, related
    amortization of debt discount, premium, and expense, other interest and that
    portion of rent expense which is estimated to be representative of the
    interest component. Preferred stock dividend requirements have been
    increased to an amount representing the pre-tax earnings required to cover
    such dividend requirements.
 
(d) The ratios of earnings to fixed charges for the twelve months ended June 30,
    1994 and for the years ended December 31, 1993, 1990 and 1989 of 0.93, 0.80,
    0.70 and (0.52), respectively, indicate that earnings were inadequate to
    cover fixed charges. The dollar amounts of the coverage deficiency for the
    twelve months ended June 30, 1994, and for the years ended 1993, 1990 and
    1989 were approximately $13 million, $37 million, $68 million and $375
    million, respectively. Excluding the loss on disallowed plant costs of $200
    million, net of income taxes, recorded in the
 
                                       S-5
   6
    third quarter of 1993, the ratio of earnings to fixed charges would have
    been 2.42 for the twelve months ended June 30, 1994 and 2.25 for the year
    ended 1993. Excluding the loss on disallowed plant costs of $137 million,
    net of income taxes, recorded in the fourth quarter of 1990, the ratio of
    earnings to fixed charges would have been 1.41 for the year ended 1990.
    Excluding the loss on disallowed plant costs of $346 million, net of income
    taxes, recorded in the first quarter of 1989, the ratio of earnings to fixed
    charges would have been 1.31 for the year ended 1989.
 
(e) The ratios of earnings to combined fixed charges and preferred stock
    dividend requirements for the twelve months ended June 30, 1994 and for the
    years ended December 31, 1993, 1990 and 1989 of 0.82, 0.70, 0.60 and (0.45),
    respectively, indicate that earnings were inadequate to cover combined fixed
    charges and preferred stock dividend requirements. The dollar amounts of the
    coverage deficiency for the twelve months ended June 30, 1994, and for the
    years ended 1993, 1990 and 1989 were approximately $38 million, $63 million,
    $105 million and $412 million, respectively. Excluding the loss on
    disallowed plant costs of $200 million, net of income taxes, recorded in the
    third quarter of 1993, the ratio of earnings to combined fixed charges and
    preferred stock dividend requirements would have been 1.98 for the twelve
    months ended June 30, 1994 and 1.83 for the year ended 1993. Excluding the
    loss on disallowed plant costs of $137 million, net of income taxes,
    recorded in the fourth quarter of 1990, the ratio of earnings to combined
    fixed charges and preferred stock dividend requirements would have been 1.09
    for the year ended 1990. Excluding the loss on disallowed plant costs of
    $346 million, net of income taxes, recorded in the first quarter of 1989,
    the ratio of earnings to combined fixed charges and preferred stock dividend
    requirements would have been 1.06 for the year ended 1989.
 
                                       S-6
   7
 
                DESCRIPTION OF THE SERIES A PREFERRED SECURITIES
 
GENERAL
 
     All of the partner interests in Illinois Power Capital, other than the
Series A Preferred Securities offered hereby, are owned by the General Partner.
The Partnership Agreement authorizes and creates the Series A Preferred
Securities, which represent limited partner interests in Illinois Power Capital
(the "Preferred Securities"). Preferred Securities may be issued from time to
time in one or more series as described in the accompanying Prospectus. The
limited partner interests represented by the Series A Preferred Securities will
have a preference with respect to dividends and amounts payable on liquidation
over the General Partner's interest in Illinois Power Capital. The Partnership
Agreement does not permit the issuance of any Preferred Securities ranking, as
to participation in profits and dividends and in the assets of Illinois Power
Capital, senior or junior to the Series A Preferred Securities or the incurrence
of any indebtedness by Illinois Power Capital. The summary of certain terms and
provisions of the Series A Preferred Securities set forth below does not purport
to be complete and is subject to, and qualified in its entirety by reference to,
the Partnership Agreement and the Partnership Act.
 
DIVIDENDS
 
     The dividends payable on each Series A Preferred Security will be fixed at
a rate per annum of      % of the liquidation preference of $25 per Preferred
Security. Dividends in arrears for more than one month will bear interest
thereon at the rate per annum of      % thereof. The term "dividends" as used
herein includes any such interest payable unless otherwise stated. The amount of
dividends payable for any period will be computed on the basis of a 360-day year
of twelve 30-day months.
 
     Dividends on the Series A Preferred Securities will be cumulative, will
accrue from the date of initial issuance and will be payable monthly in arrears,
on the last day of each calendar month of each year, commencing        , 1994,
when, as and if available and determined to be so payable by the General
Partner, except as otherwise described below. The Company has the right under
the Indenture to extend the interest payment period from time to time on the
Series A Subordinated Debentures to a period not exceeding 60 consecutive
months, and, as a consequence, monthly dividends on the Series A Preferred
Securities would be deferred (but would continue to accrue with interest) by
Illinois Power Capital during any such extended interest payment period. In the
event that the Company exercises this right, the Company may not declare or pay
dividends on, or redeem, purchase or acquire, any of its capital stock. Prior to
the termination of any such extension period, the Company may further extend the
interest payment period, provided that such extension period together with all
such previous and further extensions thereof may not exceed 60 consecutive
months. Upon the termination of any extension period and the payment of all
amounts then due, the Company may select a new extension period, subject to the
above requirements. See "Description of the Series A Subordinated Debentures --
Interest" and "-- Option to Extend Interest Payment Period."
 
     Dividends on the Series A Preferred Securities must be paid on the dates
payable to the extent that Illinois Power Capital has (i) funds legally
available for the payment of such dividends and (ii) cash on hand sufficient to
permit such payments. It is anticipated that Illinois Power Capital's earnings
available for distribution to the holders of the Series A Preferred Securities
will be limited to payments under the Series A Subordinated Debentures in which
Illinois Power Capital will invest the proceeds from the issuance and sale of
the Series A Preferred Securities and the General Partner's capital
contribution. See "Description of the Series A Subordinated Debentures." The
payment of dividends, out of moneys held by Illinois Power Capital, is
guaranteed by the Company as set forth under "Description of the Guarantee" in
the accompanying Prospectus.
 
     Dividends on the Series A Preferred Securities will be payable to the
holders thereof as they appear on the books and records of Illinois Power
Capital on the relevant record dates, which, as long as the Series A Preferred
Securities remain in book-entry-only form, will be one Business Day (as defined
below) prior to the relevant payment dates. Subject to any applicable laws and
regulations and the provisions of the Partnership Agreement, each such payment
will be made as described under
 
                                       S-7
   8
 
"Book-Entry-Only Issuance -- The Depository Trust Company" below. In the event
the Series A Preferred Securities shall not continue to remain in
book-entry-only form, the General Partner shall have the right to select
relevant record dates which shall be more than one Business Day prior to the
relevant payment dates. In the event that any date on which dividends are
payable on the Series A Preferred Securities is not a Business Day, then payment
of the dividends payable on such date will be made on the next succeeding day
which is a Business Day (and without any interest or other payment in respect of
any such delay) except that, if such Business Day is in the next succeeding
calendar year, such payment shall be made on the immediately preceding Business
Day, in each case with the same force and effect as if made on such date. A
"Business Day" shall mean any day other than a day on which banking institutions
in The City of New York are authorized or required by law to close.
 
CERTAIN RESTRICTIONS ON ILLINOIS POWER CAPITAL
 
     If dividends have not been paid in full on the Series A Preferred
Securities, Illinois Power Capital shall not:
 
          (i) pay, or set aside for payment, any dividends on any other series
     of Preferred Securities, unless the amount of any dividends paid or set
     aside on any other series of Preferred Securities is paid or set aside on
     such other series of Preferred Securities and the Series A Preferred
     Securities on a pro rata basis on the date such dividends are paid or set
     aside on such other series of Preferred Securities, so that
 
             (x) the aggregate amount of dividends paid on the Series A
        Preferred Securities bears to the aggregate amount of dividends paid on
        such other series of Preferred Securities the same ratio as
 
             (y) the aggregate of all accumulated and unpaid dividends in
        respect of the Series A Preferred Securities bears to the aggregate of
        all accumulated and unpaid dividends in respect of such other series of
        Preferred Securities; or
 
          (ii) redeem, purchase or otherwise acquire any other Preferred
     Securities;
 
until, in each case, such time as all accumulated and unpaid dividends on the
Series A Preferred Securities shall have been paid in full for all dividend
periods terminating on or prior to, in the case of clause (i), such payment and,
in the case of clause (ii), the date of such redemption, purchase or
acquisition.
 
     As of the date of this Prospectus Supplement, there are no series of
Preferred Securities outstanding.
 
OPTIONAL REDEMPTION
 
     The Series A Preferred Securities are redeemable, at the option of Illinois
Power Capital, in whole or in part, from time to time, on or after             ,
1999, upon not less than 30 nor more than 60 days' notice, at the Redemption
Price; provided, however, that prior to giving any such notice of redemption,
Illinois Power Capital shall have received from the Company a notice of
redemption of Series A Subordinated Debentures in an aggregate principal amount
equal to the aggregate liquidation preference of the Series A Preferred
Securities to be redeemed. In the event that fewer than all the outstanding
Series A Preferred Securities are to be so redeemed, the Series A Preferred
Securities to be redeemed will be selected as described under "Book-Entry-Only
Issuance -- The Depository Trust Company" below. If a partial redemption would
result in the delisting of the Series A Preferred Securities, Illinois Power
Capital may only redeem the Series A Preferred Securities in whole.
 
SPECIAL EVENT REDEMPTION OR DISTRIBUTION
 
     Subject to the next succeeding sentence, if a Tax Event or an Investment
Company Event (each, as defined below, and, each, a "Special Event") shall occur
and be continuing, the General Partner shall elect to either (i) cause Illinois
Power Capital to redeem the Series A Preferred Securities in whole (and not in
part), upon not less than 30 or more than 60 days' notice at the Redemption
Price within 90 days
 
                                       S-8
   9
 
following the occurrence of such Special Event; provided, that, if at the time
there is available to the General Partner the opportunity to eliminate, within
such 90-day period, the Special Event by taking some ministerial action, such as
filing a form or making an election, or pursuing some other similar reasonable
measure, which has no adverse effect on Illinois Power Capital or the General
Partner, the General Partner will pursue such measure in lieu of redemption, or
(ii) dissolve Illinois Power Capital and, after satisfaction of liabilities of
creditors as required by the Partnership Act, cause Series A Subordinated
Debentures to be distributed to the holders of the Series A Preferred Securities
in liquidation of their interests in Illinois Power Capital, within 90 days
following the occurrence of such Special Event. In the case of a Tax Event, the
General Partner may also elect to cause the Series A Preferred Securities to
remain outstanding.
 
     In the event of a distribution of Series A Subordinated Debentures as
described in (ii) above, each holder of Series A Preferred Securities would
receive Series A Subordinated Debentures in an aggregate principal amount equal
to the aggregate liquidation preference of $25 per Series A Preferred Security
on the Series A Preferred Securities held by it, with such Series A Subordinated
Debentures bearing interest at a rate per annum equal to the dividend rate per
annum on such Series A Preferred Securities from the last date on which
dividends were paid.
 
     "Tax Event" means that the General Partner shall have obtained an opinion
of nationally recognized independent tax counsel experienced in such matters to
the effect that, as a result of (a) any amendment to, or change (including any
announced prospective change) in, the laws (or any regulations thereunder) of
the United States or any political subdivision or taxing authority thereof or
therein, (b) any amendment to or change in an interpretation or application of
such laws or regulations by any legislative body, court, governmental agency or
regulatory authority (including the enactment of any legislation and the
publication of any judicial decision or regulatory determination on or after
such date) or (c) any interpretation or pronouncement that provides for a
position with respect to such laws or regulations that differs from the
generally accepted position on        , 1994, which amendment or change is
effective or such interpretation or pronouncement is announced on or after
       , 1994, there is more than an insubstantial risk that (i) Illinois Power
Capital is subject to federal income tax with respect to interest received on
the Series A Subordinated Debentures, (ii) interest payable to Illinois Power
Capital on the Series A Subordinated Debentures will not be deductible for
federal income tax purposes or (iii) Illinois Power Capital is subject to more
than a de minimis amount of other taxes, duties or other governmental charges.
 
     "Investment Company Event" means the occurrence of a change in law or
regulation or a written change in interpretation or application of law or
regulation by any legislative body, court, governmental agency or regulatory
authority (a "Change in 1940 Act Law") to the effect that Illinois Power Capital
is or will be considered an "investment company" which is required to be
registered under the Investment Company Act of 1940, as amended (the "1940
Act"), which Change in 1940 Act Law becomes effective on or after        , 1994;
provided, that no Investment Company Event shall be deemed to have occurred if
the General Partner obtains a written opinion of nationally recognized
independent counsel experienced in practice under the 1940 Act to the effect
that the General Partner has successfully issued an additional or supplemental
irrevocable and unconditional guarantee (x) of accumulated and unpaid dividends
(whether or not determined to be paid out of moneys legally available therefor)
on the Series A Preferred Securities and (y) of the full amount of the
Liquidation Distribution (as hereinafter defined) on the Series A Preferred
Securities upon a liquidation of Illinois Power Capital (regardless of the
amount of assets of Illinois Power Capital otherwise available for distribution
in such liquidation) to avoid such Change in 1940 Act Law so that in the opinion
of such counsel, notwithstanding such Change in 1940 Act Law, Illinois Power
Capital is not required to be registered as an "investment company" within the
meaning of the 1940 Act.
 
     After the date fixed for any distribution of Series A Subordinated
Debentures, upon dissolution of Illinois Power Capital, (i) the Series A
Preferred Securities will no longer be deemed to be outstanding, (ii) The
Depository Trust Company (the "Depository" or "DTC") or its nominee, as the
record holder of the Series A Preferred Securities, will receive a registered
global certificate or certificates representing
 
                                       S-9
   10
 
the Series A Subordinated Debentures to be delivered upon such distribution and
(iii) any certificates representing Series A Preferred Securities not held by
DTC or its nominee will be deemed to represent Series A Subordinated Debentures
having a principal amount equal to the aggregate liquidation preference of such
Series A Preferred Securities until such certificates are presented to the
Company or its agent for transfer or reissuance.
 
MANDATORY REDEMPTION
 
     Upon the repayment of the Series A Subordinated Debentures at maturity, or
earlier, the proceeds from such repayment will be applied to redeem the Series A
Preferred Securities, in whole, upon not less than 30 nor more than 60 days'
notice, at the Redemption Price.
 
REDEMPTION PROCEDURES
 
     Illinois Power Capital may not redeem fewer than all of the outstanding
Series A Preferred Securities unless all accumulated and unpaid dividends have
been paid on all Series A Preferred Securities for all monthly dividend periods
terminating on or prior to the date of redemption.
 
     If Illinois Power Capital gives a notice of redemption in respect of Series
A Preferred Securities (which notice will be irrevocable), then, by 12:00 noon,
New York time, on the redemption date, Illinois Power Capital will irrevocably
deposit with DTC funds sufficient to pay the applicable Redemption Price and
will give DTC irrevocable instructions and authority to pay the Redemption Price
to the holders of the Series A Preferred Securities. See "Book-Entry-Only
Issuance -- The Depository Trust Company." If notice of redemption shall have
been given and funds deposited as required, then upon the date of such deposit,
all rights of holders of such Series A Preferred Securities so called for
redemption will cease, except the right of the holders of such Series A
Preferred Securities to receive the Redemption Price, but without interest on
such Redemption Price. In the event that any date fixed for redemption of Series
A Preferred Securities is not a Business Day, then payment of the Redemption
Price payable on such date will be made on the next succeeding day which is a
Business Day (and without any interest or other payment in respect of any such
delay), except that, if such Business Day falls in the next calendar year, such
payment will be made on the immediately preceding Business Day. In the event
that payment of the Redemption Price in respect of Series A Preferred Securities
is improperly withheld or refused and not paid either by Illinois Power Capital
or by the Company pursuant to the Guarantee described under "Description of the
Guarantee" in the accompanying Prospectus, dividends on such Series A Preferred
Securities will continue to accrue at the then applicable rate, from the
original redemption date to the date of payment, in which case the actual
payment date will be considered the date fixed for redemption for purposes of
calculating the Redemption Price.
 
     Subject to the foregoing and applicable law (including, without limitation,
United States federal securities laws), the Company or its subsidiaries may at
any time and from time to time purchase outstanding Series A Preferred
Securities by tender, in the open market or by private agreement.
 
LIQUIDATION DISTRIBUTION UPON DISSOLUTION
 
     In the event of any voluntary or involuntary dissolution, winding-up or
termination of Illinois Power Capital, the holders of the Series A Preferred
Securities at the time will be entitled to receive out of the assets of Illinois
Power Capital available for distribution to partners, after satisfaction of
liabilities of creditors as required by the Partnership Act, before any
distribution of assets is made to the General Partner, but together with the
holders of every other series of Preferred Securities outstanding, an amount
equal to, in the case of holders of Series A Preferred Securities, the aggregate
of the liquidation preference of $25 per Series A Preferred Security and all
accumulated and unpaid dividends thereon to the date of payment (the
"Liquidation Distribution"), unless, in connection with such dissolution,
winding-up or termination, Series A Subordinated Debentures in an aggregate
principal amount equal to $25 per Series A Preferred Security have been
distributed on a pro rata basis to the holders of the Series A Preferred
Securities.
 
                                      S-10
   11
 
     If, upon any such dissolution, the Liquidation Distribution can be paid
only in part because Illinois Power Capital has insufficient assets available to
pay in full the aggregate Liquidation Distribution and the aggregate maximum
liquidation distributions on any other series of Preferred Securities, then the
amounts payable directly by Illinois Power Capital on the Series A Preferred
Securities and on such other series of Preferred Securities shall be paid on a
pro rata basis, so that
 
          (i) the aggregate amount paid in respect of the Liquidation
     Distribution bears to the aggregate amount paid as liquidation
     distributions on the other series of Preferred Securities the same ratio as
 
          (ii) the aggregate Liquidation Distribution bears to the aggregate
     maximum liquidation distributions on the other series of Preferred
     Securities.
 
     Pursuant to the Partnership Agreement, Illinois Power Capital shall be
dissolved and its affairs shall be wound up: (i) upon the expiration of the term
of Illinois Power Capital on December 31, 2047, (ii) upon the bankruptcy or
withdrawal of the General Partner, (iii) upon the assignment by the General
Partner of its entire interest in Illinois Power Capital when the assignee is
not admitted to Illinois Power Capital as a general partner of Illinois Power
Capital in accordance with the Partnership Agreement, or the filing of a
certificate of dissolution or its equivalent with respect to the General
Partner, or the revocation of the General Partner's charter and the expiration
of 90 days after the date of notice to the General Partner of revocation without
a reinstatement of its charter, or any other event occurs which causes the
General Partner to cease to be a general partner of Illinois Power Capital under
the Partnership Act, unless the business of Illinois Power Capital is continued
in accordance with the Partnership Act, (iv) in accordance with the provisions
of the Series A Preferred Securities, (v) upon the entry of a decree of a
judicial dissolution or (vi) upon the written consent of all partners of
Illinois Power Capital.
 
MERGER, CONSOLIDATION OR AMALGAMATION OF ILLINOIS POWER CAPITAL
 
     Illinois Power Capital may not consolidate, amalgamate, merge with or into,
or be replaced by, or convey, transfer or lease its properties and assets
substantially as an entirety to any corporation or other body, except as
described below. Illinois Power Capital may, without the consent of the holders
of the Series A Preferred Securities, consolidate, amalgamate, merge with or
into, or be replaced by a limited liability company, a limited partnership or a
trust organized as such under the laws of any state of the United States;
provided, that (i) such successor entity either (x) expressly assumes all of the
obligations of Illinois Power Capital under the Series A Preferred Securities or
(y) substitutes for the Series A Preferred Securities other securities having
substantially the same terms as the Series A Preferred Securities (the
"Successor Securities") so long as the Successor Securities rank, with respect
to participation in the profits and dividends or in the assets of the successor
entity, at least as high as the Series A Preferred Securities rank with respect
to participation in the profits and dividends or in the assets of Illinois Power
Capital, (ii) the Company expressly acknowledges such successor entity as the
holder of the Series A Subordinated Debentures, (iii) the Series A Preferred
Securities or any Successor Securities are listed, or any Successor Securities
will be listed upon notification of issuance, on any national securities
exchange or other organization on which the Series A Preferred Securities are
then listed, (iv) such merger, consolidation, amalgamation or replacement does
not cause the Series A Preferred Securities to be downgraded by any "nationally
recognized statistical rating organization," as that term is defined by the
Commission for purposes of Rule 436(g)(2) under the Securities Act, or cause any
Successor Securities to be rated lower than the Series A Preferred Securities
immediately prior to such merger, consolidation, amalgamation or replacement,
(v) such merger, consolidation, amalgamation or replacement does not adversely
affect the powers, preferences and other special rights of the holders of the
Series A Preferred Securities in any material respect, (vi) such successor
entity has a purpose substantially identical to that of Illinois Power Capital
and (vii) prior to such merger, consolidation, amalgamation or replacement, the
Company has received an opinion of nationally recognized independent counsel to
Illinois Power Capital experienced in such matters to the effect that (x) such
successor entity will be treated as a partnership for federal income tax
purposes, (y) following such merger, consolidation, amalgamation or replacement,
the Company and such successor entity will be in compliance with the 1940 Act
without registering thereunder as an investment company and (z) such
 
                                      S-11
   12
 
merger, consolidation, amalgamation or replacement will not adversely affect the
limited liability of the holders of the Series A Preferred Securities.
 
VOTING RIGHTS
 
     Except as provided below and under "Description of the Guarantee --
Amendments and Assignment" in the accompanying Prospectus and as otherwise
required by law and the Partnership Agreement, the holders of the Series A
Preferred Securities will have no voting rights.
 
     If (i) Illinois Power Capital fails to pay dividends in full on the Series
A Preferred Securities for 18 consecutive monthly dividend periods; (ii) an
Event of Default (as defined in the Indenture) occurs and is continuing on the
Series A Subordinated Debentures; or (iii) the Company is in default on any of
its payment or other obligations under the Guarantee (as described under
"Description of the Guarantee -- Certain Covenants of the Company" in the
accompanying Prospectus), then the holders of the Series A Preferred Securities,
together with the holders of any other series of Preferred Securities having the
right to vote for the appointment of a special representative of Illinois Power
Capital and the limited partners (a "Special Representative") in such event,
acting as a single class, will be entitled by the vote of a majority in
liquidation preference of the Preferred Securities to appoint and authorize a
Special Representative to enforce Illinois Power Capital's creditor rights under
the Series A Subordinated Debentures, to enforce the rights of the holders of
the Series A Preferred Securities under the Guarantee and to enforce the rights
of the holders of the Series A Preferred Securities to receive dividends on the
Series A Preferred Securities. The Special Representative shall not, by virtue
of acting in such capacity, be admitted as a partner in Illinois Power Capital
or otherwise be deemed to be a partner in Illinois Power Capital and shall have
no liability for the debts, obligations or liabilities of Illinois Power
Capital. For purposes of determining whether Illinois Power Capital has failed
to pay dividends in full for 18 consecutive monthly dividend periods, dividends
shall be deemed to remain in arrears, notwithstanding any payments in respect
thereof, until full cumulative dividends have been or contemporaneously are paid
with respect to all monthly dividend periods terminating on or prior to the date
of payment of such full cumulative dividends. Not later than 30 days after such
right to appoint a Special Representative arises, the General Partner will
convene a meeting for the purpose of appointing a Special Representative. If the
General Partner fails to convene such meeting within such 30-day period, the
holders of 10% in liquidation preference of the outstanding Preferred Securities
will be entitled to convene such meeting. The provisions of the Partnership
Agreement relating to the convening and conduct of the meetings of the partners
will apply with respect to any such meeting. Any Special Representative so
appointed shall cease to be a Special Representative of Illinois Power Capital
and the limited partners if Illinois Power Capital (or the Company pursuant to
the Guarantee) shall have paid in full all accumulated and unpaid dividends on
the Preferred Securities or such default or breach, as the case may be, shall
have been cured, and the General Partner shall continue the business of Illinois
Power Capital without dissolution. Notwithstanding the appointment of any such
Special Representative, the Company shall continue as General Partner and shall
retain all rights under the Indenture, including the right to extend the
interest payment period from time to time to a period not exceeding 60
consecutive months as provided under "Description of the Series A Subordinated
Debentures -- Option to Extend Interest Payment Period."
 
     If any proposed amendment to the Partnership Agreement provides for, or the
General Partner otherwise proposes to effect, (i) any action which would
adversely affect the powers, preferences or special rights of the Series A
Preferred Securities, whether by way of amendment to the Partnership Agreement
or otherwise (including, without limitation, the authorization or issuance of
any limited partner interests in Illinois Power Capital ranking, as to
participation in the profits and dividends or in the assets of Illinois Power
Capital, senior to the Series A Preferred Securities), or (ii) the dissolution,
winding-up or termination of Illinois Power Capital, other than (x) in
connection with the distribution of Series A Subordinated Debentures upon the
occurrence of a Special Event or (y) as described under "Merger, Consolidation
or Amalgamation of Illinois Power Capital" above, then the holders of
outstanding Series A Preferred Securities will be entitled to vote on such
amendment or proposal of the General Partner (but not on any other amendment or
proposal) as a class with all other holders of series of Preferred Securities
 
                                      S-12
   13
 
similarly affected, and such amendment or proposal shall not be effective except
with the approval of the holders of 66 2/3% in liquidation preference of such
outstanding Preferred Securities having a right to vote on the matter; provided,
however, that no such approval shall be required if the dissolution, winding-up
or termination of Illinois Power Capital is proposed or initiated upon the
initiation of proceedings, or after proceedings have been initiated, for the
dissolution, winding-up, liquidation or termination of the Company.
 
     The rights attached to the Series A Preferred Securities will be deemed not
to be adversely affected by the creation or issue of, and no vote will be
required for the creation of, any further limited partner interests of Illinois
Power Capital ranking pari passu with the Series A Preferred Securities with
regard to participation in the profits and dividends or in the assets of
Illinois Power Capital. Holders of Series A Preferred Securities have no
preemptive rights.
 
     So long as any Series A Subordinated Debentures are held by Illinois Power
Capital, the General Partner shall not (i) direct the time, method and place of
conducting any proceeding for any remedy available to the Trustee, or executing
any trust or power conferred on the Trustee with respect to such series, (ii)
waive any past default which is waivable under Section 6.06 of the Indenture,
(iii) exercise any right to rescind or annul a declaration that the principal of
all the Series A Subordinated Debentures shall be due and payable or (iv)
consent to any amendment, modification or termination of the Indenture, where
such consent shall be required, without, in each case, obtaining the prior
approval of the holders of at least 66 2/3% in liquidation preference of all
series of Preferred Securities affected thereby, acting as a single class;
provided, however, that where a consent under the Indenture would require the
consent of each holder affected thereby, no such consent shall be given by the
General Partner without the prior consent of each holder of all series of
Preferred Securities affected thereby. The General Partner shall not revoke any
action previously authorized or approved by a vote of any series of Preferred
Securities. The General Partner shall notify all holders of the Series A
Preferred Securities of any notice of default received from the Trustee with
respect to the Series A Subordinated Debentures.
 
     Any required approval of holders of Series A Preferred Securities may be
given at a separate meeting of holders of Preferred Securities convened for such
purpose, at a meeting of all of the partners in Illinois Power Capital or
pursuant to written consent. Illinois Power Capital will cause a notice of any
meeting at which holders of Series A Preferred Securities are entitled to vote,
or of any matter upon which action by written consent of such holders is to be
taken, to be mailed to each holder of record of Series A Preferred Securities.
Each such notice will include a statement setting forth (i) the date of such
meeting or the date by which such action is to be taken, (ii) a description of
any resolution proposed for adoption at such meeting on which such holders are
entitled to vote or of such matter upon which written consent is sought and
(iii) instructions for the delivery of proxies or consents.
 
     No vote or consent of the holders of Series A Preferred Securities will be
required for Illinois Power Capital to redeem and cancel Series A Preferred
Securities in accordance with the Partnership Agreement.
 
     Notwithstanding that holders of Series A Preferred Securities are entitled
to vote or consent under any of the circumstances described above, any of the
Series A Preferred Securities and any other series of Preferred Securities that
are entitled to vote or consent with such Series A Preferred Securities as a
single class at such time that are owned by the Company or any entity owned more
than 50% by the Company, either directly or indirectly, shall not be entitled to
vote or consent and shall, for purposes of such vote or consent, be treated as
if they were not outstanding.
 
     Holders of the Series A Preferred Securities will have no rights to remove
or replace the General Partner.
 
BOOK-ENTRY-ONLY ISSUANCE -- THE DEPOSITORY TRUST COMPANY
 
     DTC will act as securities depository for the Series A Preferred
Securities. The Series A Preferred Securities will be issued only as
fully-registered securities registered in the name of Cede & Co. (DTC's
 
                                      S-13
   14
 
nominee). One or more fully-registered global Series A Preferred Security
certificates will be issued, representing in the aggregate the total number of
Series A Preferred Securities, and will be deposited with DTC.
 
     DTC is a limited-purpose trust company organized under the New York Banking
Law, a "banking organization" within the meaning of the New York Banking Law, a
member of the Federal Reserve System, a "clearing corporation" within the
meaning of the New York Uniform Commercial Code, and a "clearing agency"
registered pursuant to the provisions of Section 17A of the Securities Exchange
Act of 1934, as amended (the "Exchange Act"). DTC holds securities that its
participants ("Participants") deposit with DTC. DTC also facilitates the
settlement among Participants of securities transactions, such as transfers and
pledges, in deposited securities through electronic computerized book-entry
changes in Participants' accounts, thereby eliminating the need for physical
movement of securities certificates. Direct Participants include securities
brokers and dealers, banks, trust companies, clearing corporations, and certain
other organizations ("Direct Participants"). DTC is owned by a number of its
Direct Participants and by The New York Stock Exchange, Inc. (the "New York
Stock Exchange"), the American Stock Exchange, Inc., and the National
Association of Securities Dealers, Inc. Access to the DTC system is also
available to others such as securities brokers and dealers, banks and trust
companies that clear through or maintain a custodial relationship with a Direct
Participant, either directly or indirectly ("Indirect Participants"). The rules
applicable to DTC and its Participants are on file with the Commission.
 
     Purchases of Series A Preferred Securities within the DTC system must be
made by or through Direct Participants, which will receive a credit for the
Series A Preferred Securities on DTC's records. The ownership interest of each
actual purchaser of each Series A Preferred Security ("Beneficial Owner") is in
turn to be recorded on the Direct and Indirect Participants' records. Beneficial
Owners will not receive written confirmation from DTC of their purchases, but
Beneficial Owners are expected to receive written confirmations providing
details of the transactions, as well as periodic statements of their holdings,
from the Direct or Indirect Participants through which the Beneficial Owners
purchased Series A Preferred Securities. Transfers of ownership interests in the
Series A Preferred Securities are to be accomplished by entries made on the
books of Participants acting on behalf of Beneficial Owners. Beneficial Owners
will not receive certificates representing their ownership interests in Series A
Preferred Securities, except in the event that use of the book-entry system for
the Series A Preferred Securities is discontinued.
 
     DTC has no knowledge of the actual Beneficial Owners of the Series A
Preferred Securities; DTC's records reflect only the identity of the Direct
Participants to whose accounts such Series A Preferred Securities are credited,
which may or may not be the Beneficial Owners. The Participants will remain
responsible for keeping account of their holdings on behalf of their customers.
 
     Conveyance of notices and other communications by DTC to Direct
Participants, by Direct Participants to Indirect Participants, and by Direct
Participants and Indirect Participants to Beneficial Owners will be governed by
arrangements among them, subject to any statutory or regulatory requirements as
may be in effect from time to time.
 
     Redemption notices shall be sent to Cede & Co. If less than all of the
Series A Preferred Securities are being redeemed, DTC's practice is to determine
by lot the amount of the interest of each Direct Participant in such series to
be redeemed.
 
     Although voting with respect to the Series A Preferred Securities is
limited, in those cases where a vote is required, neither DTC nor Cede & Co.
will itself consent or vote with respect to Series A Preferred Securities. Under
its usual procedures, DTC would mail an Omnibus Proxy to Illinois Power Capital
as soon as possible after the record date. The Omnibus Proxy assigns Cede &
Co.'s consenting or voting rights to those Direct Participants to whose accounts
the Series A Preferred Securities are credited on the record date (identified in
a listing attached to the Omnibus Proxy).
 
     Dividend payments on the Series A Preferred Securities will be made to DTC.
DTC's practice is to credit Direct Participants' accounts on the relevant
payment date in accordance with their respective
 
                                      S-14
   15
 
holdings shown on DTC's records unless DTC has reason to believe that it will
not receive payments on such payment date. Payments by Participants to
Beneficial Owners will be governed by standing instructions and customary
practices and will be the responsibility of such Participant and not of DTC,
Illinois Power Capital or the Company, subject to any statutory or regulatory
requirements as may be in effect from time to time. Payment of dividends to DTC
is the responsibility of Illinois Power Capital, disbursement of such payments
to Direct Participants is the responsibility of DTC, and disbursement of such
payments to the Beneficial Owners is the responsibility of Direct and Indirect
Participants.
 
     DTC may discontinue providing its services as securities depository with
respect to the Series A Preferred Securities at any time by giving reasonable
notice to Illinois Power Capital. Under such circumstances, in the event that a
successor securities depository is not obtained, Series A Preferred Security
certificates are required to be printed and delivered. Additionally, Illinois
Power Capital (with the consent of the Company) may decide to discontinue use of
the system of book-entry transfers through DTC (or a successor depository). In
that event, certificates for the Series A Preferred Securities will be printed
and delivered. In each of the above circumstances, the General Partner will
appoint a paying agent with respect to the Series A Preferred Securities.
 
     The information in this section concerning DTC and DTC's book-entry system
has been obtained from sources that Illinois Power Capital believes to be
reliable, but Illinois Power Capital takes no responsibility for the accuracy
thereof.
 
REGISTRAR AND TRANSFER AGENT
 
     The Company will act as registrar and transfer agent for the Series A
Preferred Securities.
 
     Registration of transfers of Series A Preferred Securities will be effected
without charge by or on behalf of Illinois Power Capital, but upon payment (with
the giving of such indemnity as Illinois Power Capital or the Company may
require) in respect of any tax or other governmental charges which may be
imposed in relation to it.
 
     Illinois Power Capital will not be required to register or cause to be
registered the transfer of Series A Preferred Securities after such Series A
Preferred Securities have been called for redemption.
 
MISCELLANEOUS
 
     Application has been made to list the Series A Preferred Securities on the
New York Stock Exchange.
 
     The General Partner is authorized and directed to conduct its affairs and
to operate Illinois Power Capital in such a way that (i) Illinois Power Capital
will not be deemed to be an "investment company" required to be registered under
the 1940 Act, (ii) Illinois Power Capital will be taxed as a partnership for
federal income tax purposes and (iii) the Series A Subordinated Debentures will
be treated as indebtedness of the Company for federal income tax purposes. In
this connection, the General Partner is authorized to take any action, not
inconsistent with applicable law, the certificate of limited partnership or the
Partnership Agreement, that the General Partner determines in its discretion to
be necessary or desirable for such purposes, as long as such action does not
adversely affect the interests of the holders of the Series A Preferred
Securities.
 
                                      S-15
   16
 
              DESCRIPTION OF THE SERIES A SUBORDINATED DEBENTURES
 
     Set forth below is a description of the specific terms of the Series A
Subordinated Debentures in which Illinois Power Capital will invest with (i) the
proceeds of the issuance and sale of the Series A Preferred Securities and (ii)
the General Partner's capital contribution with respect to the Series A
Preferred Securities (the "General Partnership Payment"). This description
supplements the description of the general terms and provisions of the
Subordinated Debentures set forth in the accompanying Prospectus under the
caption "Description of the Subordinated Debentures." The following description
does not purport to be complete and is qualified in its entirety by reference to
the description in the accompanying Prospectus and the Indenture between the
Company and The First National Bank of Chicago, as Trustee, as supplemented by a
First Supplemental Indenture (the Indenture, as so supplemented, is hereinafter
referred to as the "Indenture").
 
     Under certain circumstances involving the dissolution of Illinois Power
Capital following the occurrence of a Special Event, Series A Subordinated
Debentures may be distributed to the holders of the Series A Preferred
Securities in liquidation of Illinois Power Capital. See "Description of the
Series A Preferred Securities -- Special Event Redemption or Distribution."
 
GENERAL
 
     The Series A Subordinated Debentures will be issued as a series of
Subordinated Debentures under the Indenture. The Series A Subordinated
Debentures will be limited in aggregate principal amount to approximately
$      million, such amount being the sum of the aggregate liquidation
preference of the Series A Preferred Securities and the General Partnership
Payment.
 
     The entire principal amount of the Series A Subordinated Debentures will
become due and payable, together with any accrued and unpaid interest thereon,
including Additional Interest (as hereinafter defined), if any, on
               , 2043.
 
     The Series A Subordinated Debentures if distributed to holders of Series A
Preferred Securities upon the dissolution of Illinois Power Capital will
initially be so issued as a Global Security (as defined below). As described
herein, under certain limited circumstances Series A Subordinated Debentures may
be issued in certificated form in exchange for a Global Security. See
"Book-Entry and Settlement" below. In the event that Series A Subordinated
Debentures are issued in certificated form, such Series A Subordinated
Debentures will be in denominations of $25 and integral multiples thereof and
may be transferred or exchanged at the offices described below.
 
     Payments on Series A Subordinated Debentures issued as a Global Security
will be made to DTC, as the depository for the Series A Subordinated Debentures.
In the event Series A Subordinated Debentures are issued in certificated form,
principal and interest will be payable, the transfer of the Series A
Subordinated Debentures will be registrable and the Series A Subordinated
Debentures will be exchangeable for Series A Subordinated Debentures of other
denominations of a like aggregate principal amount at the corporate trust office
of the Trustee in The City of New York; provided, that payment of interest may
be made at the option of the Company by check mailed to the address of the
persons entitled thereto.
 
     If the Series A Subordinated Debentures are distributed to the holders of
Series A Preferred Securities upon the dissolution of Illinois Power Capital,
the Company will use its best efforts to list the Series A Subordinated
Debentures on the New York Stock Exchange or on such other exchange as the
Series A Preferred Securities are then listed and traded on the same part of any
such exchange.
 
MANDATORY PREPAYMENT
 
     If Illinois Power Capital redeems Series A Preferred Securities in
accordance with the terms thereof, the Series A Subordinated Debentures will
become due and payable in a principal amount equal to the aggregate liquidation
preference of the Series A Preferred Securities so redeemed, together with all
accrued and unpaid interest, including Additional Interest, if any. Any payment
pursuant to this provision
 
                                      S-16
   17
 
shall be made prior to 12:00 noon, New York time, on the date of such redemption
or at such other time on such earlier date as the parties thereto shall agree.
 
OPTIONAL REDEMPTION
 
     The Company shall have the right to redeem the Series A Subordinated
Debentures, in whole or in part, from time to time, on or after                ,
1999, upon not less than 30 nor more than 60 days' notice, at a redemption price
equal to 100% of the principal amount to be redeemed plus any accrued and unpaid
interest, including Additional Interest, if any, to the redemption date.
 
INTEREST
 
     Each Series A Subordinated Debenture will bear interest at the rate of
     % per annum from the original date of issuance until the principal of such
Series A Debenture becomes due and payable, and on any overdue principal and (to
the extent that payment of such interest is enforceable under applicable law) on
any overdue installment of interest at the same rate per annum, payable monthly
in arrears on the last day of each calendar month of each year (each, an
"Interest Payment Date"), commencing                , 1994, to the person in
whose name such Series A Subordinated Debenture is registered, subject to
certain exceptions, at the close of business on the Business Day next preceding
such Interest Payment Date. In the event the Series A Subordinated Debentures
shall not continue to remain in book-entry-only form, the Company shall have the
right to select record dates which shall be more than one Business Day prior to
the Interest Payment Date.
 
     The amount of interest payable for any period will be computed on the basis
of a 360-day year of twelve 30-day months and for any period shorter than a full
month on the basis of actual days elapsed in such period. In the event that any
date on which interest is payable on the Series A Subordinated Debentures is not
a Business Day, then payment of the interest payable on such date will be made
on the next succeeding day which is a Business Day (and without any interest or
other payment in respect of any such delay), except that, if such Business Day
is in the next succeeding calendar year, such payment shall be made on the
immediately preceding Business Day, in each case with the same force and effect
as if made on such date.
 
OPTION TO EXTEND INTEREST PAYMENT PERIOD
 
     So long as the Company is not in default in the payment of interest on any
series of Subordinated Debentures issued under the Indenture, the Company shall
have the right at any time during the term of the Series A Subordinated
Debentures to extend the interest payment period from time to time to a period
not exceeding 60 consecutive months (the "Extension Period"), at the end of
which Extension Period the Company shall pay all interest then accrued and
unpaid (together with interest thereon at the rate specified for the Series A
Subordinated Debentures to the extent permitted by applicable law); provided,
that, during any such Extension Period, the Company shall not declare or pay any
dividend on, or redeem, purchase, acquire or make a liquidation payment with
respect to, any of its capital stock or make any guarantee payments with respect
to the foregoing (other than payments on the Guarantee); and provided further
that any such extended interest payment period may only be selected with respect
to the Series A Subordinated Debentures if an extended interest payment period
of identical length is simultaneously selected for all Subordinated Debentures
then outstanding under the Indenture. Prior to the termination of any such
Extension Period, the Company may further extend the interest payment period,
provided that such Extension Period together with all such previous and further
extensions thereof may not exceed 60 consecutive months. Upon the termination of
any Extension Period and the payment of all amounts then due, the Company may
select a new Extension Period, subject to the above requirements. No interest
shall be due and payable during an Extension Period, except at the end thereof.
 
     If Illinois Power Capital shall be the sole holder of the Series A
Subordinated Debentures, the Company shall give Illinois Power Capital and the
Trustee notice of its selection of such Extension Period one Business Day prior
to the earlier of (i) the next succeeding date on which the dividends on the
Series A Preferred Securities are payable or (ii) the date Illinois Power
Capital is required to give notice to the New York Stock Exchange or other
applicable self-regulatory organization or to holders of the
 
                                      S-17
   18
 
Series A Preferred Securities of the record date or the date such dividend is
payable, but in any event not less than one Business Day prior to such record
date. The Company shall cause Illinois Power Capital to give notice of the
Company's selection of such Extension Period to the holders of the Series A
Preferred Securities. If Illinois Power Capital shall not be the sole holder of
the Series A Subordinated Debentures, the Company shall give the holders of the
Series A Subordinated Debentures and the Trustee notice of its selection of such
Extension Period ten Business Days prior to the earlier of (i) the next
succeeding Interest Payment Date or (ii) the date the Company is required to
give notice to the New York Stock Exchange or other applicable self-regulatory
organization, or to holders of the Series A Subordinated Debentures, of the
record or payment date of such related interest payment, but in any event not
less than two Business Days prior to such record date.
 
ADDITIONAL INTEREST
 
     So long as any Subordinated Debentures remain outstanding, if at any time
Illinois Power Capital shall be required to pay any interest on dividends in
arrears in respect of the Series A Preferred Securities pursuant to the terms
thereof, then the Company will pay as interest to Illinois Power Capital as the
holder of the Series A Subordinated Debentures ("Additional Interest") an amount
equal to such interest on dividends in arrears. In addition, if Illinois Power
Capital would be required to pay any taxes, duties, assessments or governmental
charges of whatever nature (other than withholding taxes) imposed by the United
States, or any other taxing authority, then, in any such case, the Company also
will pay as Additional Interest such amounts as shall be required so that the
net amounts received and retained by Illinois Power Capital after paying any
such taxes, duties, assessments or governmental charges will be not less than
the amounts Illinois Power Capital would have received had no such taxes,
duties, assessments or governmental charges been imposed.
 
SET-OFF
 
     Notwithstanding anything to the contrary in the Indenture, the Company
shall have the right to set-off any payment it is otherwise required to make
thereunder with and to the extent the Company has theretofore made, or is
concurrently on the date of such payment making, a payment under the Guarantee.
 
EVENTS OF DEFAULT
 
     In the case any Event of Default (as defined in the Indenture) shall occur
and be continuing, the Trustee or the holders of not less than 25% in principal
amount of the outstanding Subordinated Debentures will have the right to declare
the principal of the Series A Subordinated Debentures to be forthwith due and
payable and to enforce Illinois Power Capital's other rights as a creditor with
respect to the Series A Subordinated Debentures. See "Enforcement of Certain
Rights by Special Representative" below for a discussion of certain rights
available to holders of the Series A Preferred Securities upon the occurrence of
an Event of Default.
 
ENFORCEMENT OF CERTAIN RIGHTS BY SPECIAL REPRESENTATIVE
 
     If (i) Illinois Power Capital fails to pay dividends in full on the Series
A Preferred Securities for 18 consecutive monthly dividend periods; (ii) an
Event of Default occurs and is continuing on the Series A Subordinated
Debentures; or (iii) the Company is in default on any of its payment or other
obligations under the Guarantee, under the terms of the Series A Preferred
Securities, the holders of outstanding Series A Preferred Securities will have
the rights referred to under "Description of the Series A Preferred Securities
- -- Voting Rights," including the right to appoint a Special Representative,
which Special Representative shall be authorized to exercise Illinois Power
Capital's right to accelerate the principal amount of the Series A Subordinated
Debentures and to enforce Illinois Power Capital's other creditor rights under
the Series A Subordinated Debentures. Notwithstanding the appointment of any
such Special Representative, the Company shall continue as General Partner and
shall retain all rights under
 
                                      S-18
   19
 
the Indenture, including the right to extend the interest payment period from
time to time to a period not exceeding 60 consecutive months.
 
BOOK-ENTRY AND SETTLEMENT
 
     If distributed to holders of Series A Preferred Securities in connection
with the dissolution of Illinois Power Capital as a result of the occurrence of
a Special Event, the Series A Subordinated Debentures will be issued in the form
of one or more global certificates (each, a "Global Security") registered in the
name of a nominee of DTC. Except under the limited circumstances described
below, Series A Subordinated Debentures represented by the Global Security will
not be exchangeable for, and will not otherwise be issuable as, Series A
Subordinated Debentures in definitive form. The Global Securities described
above may not be transferred except by DTC to a nominee of DTC or by a nominee
of DTC to DTC or another nominee of DTC or to a successor depository or its
nominee.
 
     The laws of some jurisdictions require that certain purchasers of
securities take physical delivery of such securities in definitive form. Such
laws may impair the ability to transfer beneficial interests in such a Global
Security.
 
     Except as provided below, owners of beneficial interests in such a Global
Security will not be entitled to receive physical delivery of Series A
Subordinated Debentures in definitive form and will not be considered the
Holders (as defined in the Indenture) thereof for any purpose under the
Indenture, and no Global Security representing Series A Subordinated Debentures
shall be exchangeable, except for another Global Security of like denomination
and tenor to be registered in the name of DTC or its nominee or to a successor
depository or its nominee. Accordingly, each beneficial owner must rely on the
procedures of DTC and, if such person is not a Participant, on the procedures of
the Participant through which such person owns its interest, to exercise any
rights of a Holder under the Indenture.
 
     THE DEPOSITORY. DTC will act as security depository for the Series A
Subordinated Debentures. For a description of DTC and the specific terms of the
depository arrangements, see "Description of the Series A Preferred Securities
- -- Book-Entry-Only Issuance -- The Depository Trust Company." As of the date of
this Prospectus Supplement, the description therein of DTC's book-entry system
and DTC's practices as they relate to purchases, transfers, notices and payments
with respect to the Series A Preferred Securities applies in all material
respects to any debt obligations represented by one or more Global Securities
held by DTC.
 
     Neither the Company, the Trustee, any paying agent nor any other agent of
the Company or the Trustee will have any responsibility or liability for any
aspect of the records relating to or payments made on account of beneficial
ownership interests in a Global Security for such Series A Subordinated
Debentures or for maintaining, supervising or reviewing any records relating to
such beneficial ownership interests.
 
     DISCONTINUANCE OF THE DEPOSITORY'S SERVICES. A Global Security shall be
exchangeable for Series A Subordinated Debentures registered in the names of
persons other than DTC or its nominee only if (i) DTC notifies the Company that
it is unwilling or unable to continue as a depository for such Global Security
and no successor depository shall have been appointed, or if any time DTC ceases
to be a clearing agency registered under the Exchange Act at a time when DTC is
required to be so registered to act as such depository, or (ii) the Company in
its sole discretion determines that such Global Security shall be so
exchangeable. Any Global Security that is exchangeable pursuant to the preceding
sentence shall be exchangeable for Series A Subordinated Debentures registered
in such names as the Depository shall direct. It is expected that such
instructions will be based upon directions received by the Depository from its
Participants with respect to ownership of beneficial interests in such Global
Security.
 
                                      S-19
   20
 
MISCELLANEOUS
 
     For restrictions on certain actions of the General Partner with respect to
Series A Subordinated Debentures held by Illinois Power Capital, see
"Description of the Series A Preferred Securities -- Voting Rights."
 
                        EFFECT OF OBLIGATIONS UNDER THE
               SERIES A SUBORDINATED DEBENTURES AND THE GUARANTEE
 
     As set forth in the Partnership Agreement, the sole purpose of Illinois
Power Capital is to issue partner interests in Illinois Power Capital,
including, without limitation, the Series A Preferred Securities, and to use the
proceeds thereof to purchase the Series A Subordinated Debentures or other
similar debt securities of the Company.
 
     As long as payments of interest and other payments are made when due on the
Series A Subordinated Debentures, such payments will be sufficient to cover
dividends and payments due on the Series A Preferred Securities primarily
because (i) the aggregate principal amount of Series A Subordinated Debentures
will be equal to the sum of the aggregate liquidation preference of the Series A
Preferred Securities and the General Partnership Payment; (ii) the interest rate
and interest and other payment dates on the Series A Subordinated Debentures
will match the dividend rate and dividend and other payment dates for the Series
A Preferred Securities; (iii) the Partnership Agreement provides that the
Company, as General Partner, shall pay for all, and Illinois Power Capital shall
not be obligated to pay, directly or indirectly, for any, costs and expenses of
Illinois Power Capital; and (iv) the Partnership Agreement further provides that
the General Partner shall not cause or permit Illinois Power Capital to, among
other things, engage in any activity that is not consistent with the purposes of
Illinois Power Capital.
 
     If the Company fails to make interest or other payments on the Series A
Subordinated Debentures when due, the Partnership Agreement provides a mechanism
whereby the holders of the Series A Preferred Securities may appoint a Special
Representative to enforce the rights of Illinois Power Capital under the Series
A Subordinated Debentures. Payments of dividends and other payments due on the
Series A Preferred Securities out of moneys held by Illinois Power Capital are
guaranteed by the Company to the extent set forth under "Description of the
Guarantee" in the accompanying Prospectus. The Partnership Agreement also
provides, and the Company, under the Guarantee, acknowledges, that a Special
Representative may be appointed to enforce the Guarantee if the Company is in
default on any of its payment obligations under the Guarantee. In addition, if
the General Partner or the Special Representative fails to enforce the
Guarantee, a holder of a Series A Preferred Security may institute a legal
proceeding directly against the Company to enforce its rights under the
Guarantee without first instituting a legal proceeding against Illinois Power
Capital or any other person or entity.
 
     The Company and Illinois Power Capital believe that the above mechanisms
and obligations, taken together, are substantially equivalent to a full and
unconditional guarantee by the Company of payments due on the Series A Preferred
Securities.
 
                             UNITED STATES TAXATION
 
GENERAL
 
     This section is a summary of certain United States federal income tax
considerations that may be relevant to prospective purchasers of Series A
Preferred Securities and represents the opinion of Schiff Hardin & Waite, tax
counsel to the Company and Illinois Power Capital, insofar as it relates to
matters of law and legal conclusions. This section is based upon current
provisions of the Internal Revenue Code of 1986, as amended (the "Code"),
existing and proposed regulations thereunder and current
 
                                      S-20
   21
administrative rulings and court decisions, all of which are subject to change.
Subsequent changes may cause tax consequences to vary substantially from the
consequences described below.
 
     No attempt has been made in the following discussion to comment on all
United States federal income tax matters affecting purchasers of Series A
Preferred Securities. Moreover, the discussion focuses on holders of Series A
Preferred Securities who are individual citizens or residents of the United
States and has only limited application to corporations, estates, trusts or
non-resident aliens. Accordingly, each prospective purchaser of Series A
Preferred Securities should consult, and should depend on, his or her own tax
advisor in analyzing the federal, state, local and foreign tax consequences of
the purchase, ownership or disposition of Series A Preferred Securities.
 
INCOME FROM SERIES A PREFERRED SECURITIES
 
     In the opinion of Schiff Hardin & Waite, Illinois Power Capital will be
treated as a partnership for federal income tax purposes. Accordingly, each
holder of Series A Preferred Securities (a "Preferred Securityholder") will be
required to include in gross income such holder's distributive share of the net
income of Illinois Power Capital. Such income will not exceed dividends received
on such Series A Preferred Securities, except in limited circumstances as
described below under "Potential Extension of Interest Payment Period." No
portion of such income will be eligible for the dividends received deduction.
 
DISPOSITION OF SERIES A PREFERRED SECURITIES
 
     Gain or loss will be recognized on a sale (including a redemption for cash)
of Series A Preferred Securities in an amount equal to the difference between
the amount realized and the Preferred Securityholder's tax basis for the Series
A Preferred Securities sold. Gain or loss recognized by a Preferred
Securityholder on the sale or exchange of a Series A Preferred Security held for
more than one year will generally be taxable as long-term capital gain or loss.
 
RECEIPT OF SERIES A SUBORDINATED DEBENTURES UPON DISSOLUTION OF ILLINOIS POWER
CAPITAL
 
     Under certain circumstances, as described under the caption "Description of
the Series A Preferred Securities -- Special Event Redemption or Distribution,"
Series A Subordinated Debentures may be distributed to the holders of the Series
A Preferred Securities in connection with the dissolution of Illinois Power
Capital. Under current United States federal income tax law, such a distribution
would be treated as a non-taxable exchange to each holder of Series A Preferred
Securities and would result in the holder of Series A Preferred Securities
receiving an aggregate tax basis in the Series A Subordinated Debentures equal
to such holder's aggregate tax basis in its Series A Preferred Securities. A
holder's holding period in the Series A Subordinated Debentures so received in
connection with the dissolution of Illinois Power Capital would include the
period for which the Series A Preferred Securities were held by such holder.
Under a change in law, a change in legal interpretation or the other
circumstances giving rise to a Special Event, however, the dissolution of
Illinois Power Capital and the distribution of Series A Subordinated Debentures
in connection with the dissolution of Illinois Power Capital could be a taxable
event to holders of the Series A Preferred Securities. In the judgment of tax
counsel to the Company and Illinois Power Capital, the series of events which
would result in the recognition of taxable gain by holders of the Series A
Preferred Securities, by reason of a dissolution of Illinois Power Capital in
response to a Special Event, is unlikely to occur. There can be no assurance in
this regard, however.
 
ILLINOIS POWER CAPITAL INFORMATION RETURNS AND AUDIT PROCEDURES
 
     The General Partner will furnish each Series A Preferred Securityholder
with a Schedule K-1 each year setting forth such Preferred Securityholder's
allocable share of income for the prior calendar year. The General Partner is
required to furnish such schedules as soon as practicable following the end of
the year, but in any event prior to March 31.
 
     Any person who holds Series A Preferred Securities as a nominee for another
person is required to furnish to Illinois Power Capital (a) the name, address
and taxpayer identification number of the
 
                                      S-21
   22
 
beneficial owner and the nominee; (b) information as to whether the beneficial
owner is (i) a person that is not a United States person, (ii) a foreign
government, an international organization or any wholly-owned agency or
instrumentality of either of the foregoing, or (iii) a tax-exempt entity; (c)
the amount and description of Series A Preferred Securities held, acquired or
transferred for the beneficial owner; and (d) certain information including the
dates of acquisitions and transfers, means of acquisitions and transfers, and
acquisition cost for purchases, as well as the amount of net proceeds from
sales. Brokers and financial institutions are required to furnish additional
information, including whether they are United States persons and certain
information on Series A Preferred Securities they acquire, hold or transfer for
their own accounts. A penalty of $50 per failure (up to a maximum of $100,000
per calendar year) is imposed by the Code for failure to report such information
to Illinois Power Capital. The nominee is required to supply the beneficial
owners of Series A Preferred Securities with the information furnished to
Illinois Power Capital.
 
POTENTIAL EXTENSION OF INTEREST PAYMENT PERIOD
 
     Under the terms of the Indenture, the Company has the right to extend from
time to time the interest payment period on the Series A Subordinated Debentures
to a period not exceeding 60 consecutive months. In the event that the Company
exercises this right, the Company may not, among other things, declare or pay
dividends on any of its capital stock. The Company has no current intention of
extending the interest payment period on the Series A Subordinated Debentures
since it desires to continue the declaration and payment of dividends on its
capital stock. In the event that the interest payment period is extended,
Illinois Power Capital will continue to accrue income equal to the amount of the
interest payment due at the end of the Extension Period pursuant to the Code and
Treasury Regulation provisions applicable to original issue discount.
 
     Accrued income will be allocated, but not distributed, to holders of record
on the Business Day preceding the last day of each calendar month. As a result,
holders of record during an Extension Period will include interest in gross
income in advance of the receipt of cash, and any such holders who dispose of
Series A Preferred Securities prior to the record date for the payment of
dividends following such Extension Period will include interest in gross income
but will not receive any cash related thereto from Illinois Power Capital. The
tax basis of a Series A Preferred Security will be increased by the amount of
any interest that is included in income without a receipt of cash, and will be
decreased when and if such cash is subsequently received from Illinois Power
Capital. The subsequent receipt of such cash will not be includible in gross
income.
 
UNITED STATES ALIEN HOLDERS
 
     For purposes of this discussion, a "United States Alien Holder" is any
holder who or which is (i) a nonresident alien individual or (ii) a foreign
corporation, partnership, estate or trust, in either case not subject to United
States federal income tax on a net income basis in respect of a Series A
Preferred Security.
 
     Under current United States federal income tax law, subject to the
discussion below with respect to backup withholding, and assuming satisfaction
by the Company of its withholding tax obligations, if any:
 
          (i) Payments by Illinois Power Capital or any of its paying agents to
     any holder of a Series A Preferred Security who or which is a United States
     Alien Holder will not be subject to United States federal withholding tax
     provided that (a) the beneficial owner of the Series A Preferred Security
     does not actually or constructively own 10% or more of the total combined
     voting power of all classes of capital stock of the Company, (b) the
     beneficial owner of the Series A Preferred Security is not a controlled
     foreign corporation that is related to the Company or Illinois Power
     Capital through stock ownership, and (c) either: (x) the beneficial owner
     of the Series A Preferred Security certifies to Illinois Power Capital or
     its agent, under penalties of perjury, that it is a United States Alien
     Holder and provides its name and address or (y) the holder of the Series A
     Preferred Security is a securities clearing organization, bank or other
     financial institution that holds customers' securities in
 
                                      S-22
   23
 
     the ordinary course of its trade or business (a "financial institution"),
     and such holder certifies to Illinois Power Capital or its agent, under
     penalties of perjury, that such statement has been received from the
     beneficial owner by it or by a financial institution between it and the
     beneficial owner and furnishes Illinois Power Capital or its agent with a
     copy thereof; and
 
          (ii) a United States Alien Holder of a Series A Preferred Security
     will generally not be subject to United States federal withholding tax on
     any gain realized on the sale or exchange of a Series A Preferred Security
     unless such holder is present in the United States for 183 days or more in
     the taxable year of sale and either has a "tax home" in the United States
     or certain other requirements are met.
 
BACKUP WITHHOLDING AND INFORMATION REPORTING
 
     In general, information reporting requirements will apply to payments of
the proceeds of the sale of Series A Preferred Securities within the United
States to noncorporate United States holders, and "backup withholding" at a rate
of 31% will apply to such payments if the United States holder fails to provide
an accurate taxpayer identification number.
 
     Payments of the proceeds from the sale by a United States Alien Holder of
Series A Preferred Securities made to or through a foreign office of a broker
will not be subject to information reporting or backup withholding, except that,
if the broker is a United States person, a controlled foreign corporation for
United States tax purposes or a foreign person 50% or more of whose gross income
is effectively connected with a United States trade or business for a specified
three-year period, information reporting may apply to such payments. Payments of
the proceeds from the sale of Series A Preferred Securities to or through the
United States office of a broker are subject to information reporting and backup
withholding unless the holder or beneficial owner certifies as to its non-United
States status or otherwise establishes an exemption from information reporting
and backup withholding.
 
                                      S-23
   24
 
                                  UNDERWRITING
 
     Subject to the terms and conditions of the Underwriting Agreement, Illinois
Power Capital has agreed to sell to each of the several Underwriters named
below, and each of the Underwriters, for whom Goldman, Sachs & Co., Bear,
Stearns & Co. Inc., Dean Witter Reynolds Inc., A.G. Edwards & Sons, Inc.,
PaineWebber Incorporated and Salomon Brothers Inc are acting as Representatives,
has severally agreed to purchase from Illinois Power Capital the respective
number of Series A Preferred Securities set forth opposite its name below:
 


                                                                        NUMBER OF
                                                                        SERIES A
                                                                        PREFERRED
                                 UNDERWRITER                            SECURITIES
          ---------------------------------------------------------     ---------
                                                                     
          Goldman, Sachs & Co. ....................................
          Bear, Stearns & Co. Inc. ................................
          Dean Witter Reynolds Inc. ...............................
          A.G. Edwards & Sons, Inc. ...............................
          PaineWebber Incorporated.................................
          Salomon Brothers Inc ....................................
                                                                        ---------
                    Total..........................................     3,880,000
                                                                        =========

 
     Under the terms and conditions of the Underwriting Agreement, the
Underwriters are committed to take and pay for all such Series A Preferred
Securities offered hereby, if any are taken.
 
     The Underwriters propose to offer the Series A Preferred Securities in part
directly to the public at the initial public offering price set forth on the
cover page of this Prospectus Supplement, and in part to certain securities
dealers at such price less a concession of $          per Series A Preferred
Security. The Underwriters may allow, and such dealers may reallow, a concession
not in excess of $          per Series A Preferred Security to certain brokers
and dealers. After the Series A Preferred Securities are released for sale to
the public, the offering price and other selling terms may from time to time be
varied by the Representatives.
 
     As the proceeds of the sale of the Series A Preferred Securities will be
loaned to the Company, the Company has agreed in the Underwriting Agreement to
pay to the Underwriters $       per Series A Preferred Security ($       per
Series A Preferred Security sold to certain institutions) for the accounts of
the several Underwriters.
 
     The Company and Illinois Power Capital have agreed, during the period
beginning from the date of the Underwriting Agreement and continuing to and
including the earlier of (i) the date, after the closing date, on which the
distribution of the Series A Preferred Securities ceases, as determined by the
Underwriters, or (ii) 30 days after the closing date, not to offer, sell,
contract to sell, or otherwise dispose of any Series A Preferred Securities, any
limited partner interests of Illinois Power Capital, or any preferred stock or
any other securities of Illinois Power Capital or the Company which are
substantially similar to the Series A Preferred Securities, or any securities
convertible into or exchangeable for Series A Preferred Securities, limited
partner interests, preferred stock or such substantially similar securities of
either Illinois Power Capital or the Company without the prior written consent
of the Underwriters.
 
     Prior to this offering, there has been no public market for the Series A
Preferred Securities. In order to meet one of the requirements for listing the
Series A Preferred Securities on the New York Stock Exchange, the Underwriters
will undertake to sell lots of 100 or more Series A Preferred Securities to a
minimum of 400 beneficial holders.
 
                                      S-24
   25
 
                                 LEGAL OPINIONS
 
     Certain legal matters will be passed upon for the Company and Illinois
Power Capital by Schiff Hardin & Waite, Chicago, Illinois, and for the
Underwriters by Reid & Priest, New York, New York. Certain matters of Delaware
law relating to the validity of the Series A Preferred Securities will be passed
upon by Richards, Layton & Finger, P.A., Wilmington, Delaware, special Delaware
counsel to the Company and Illinois Power Capital. Schiff Hardin & Waite and
Reid & Priest may rely on the opinion of Richards, Layton & Finger, P.A. as to
certain matters of Delaware law, Schiff Hardin & Waite may rely on the opinion
of Reid & Priest as to all matters of New York law, and Reid & Priest may rely
on the opinion of Schiff Hardin & Waite as to all matters of Illinois law.
 
                                      S-25
   26
 
PROSPECTUS
 
                                  $100,000,000
 
                             ILLINOIS POWER CAPITAL
 
                              PREFERRED SECURITIES
           GUARANTEED TO THE EXTENT ILLINOIS POWER CAPITAL HAS FUNDS
                             AS SET FORTH HEREIN BY
 
                             ILLINOIS POWER COMPANY
                               ------------------
 
     Illinois Power Capital, L.P. ("Illinois Power Capital"), a Delaware limited
partnership, all of the general partner interests in which are owned by Illinois
Power Company (the "Company"), may offer, from time to time, its preferred
securities, representing limited partner interests ("Preferred Securities"), in
one or more series. The payment of periodic cash distributions ("dividends")
with respect to Preferred Securities of any series, out of funds held by
Illinois Power Capital and legally available therefor, and payments on
liquidation or redemption with respect to the Preferred Securities are
guaranteed by the Company to the extent described herein (the "Guarantee"). The
Company's obligations under the Guarantee are subordinate and junior in right of
payment to all other liabilities of the Company. Subordinated Deferrable
Interest Debentures of the Company ("Subordinated Debentures") will also be
issued and sold from time to time in one or more series by the Company to
Illinois Power Capital in connection with the investment of the proceeds from
the offering of Preferred Securities. Subordinated Debentures subsequently may
be distributed to holders of Preferred Securities in connection with a
dissolution of Illinois Power Capital upon the occurrence of certain events as
may be described in an accompanying Prospectus Supplement (a "Prospectus
Supplement"). The Subordinated Debentures will be unsecured and subordinate and
junior in right of payment to all present and future Senior Indebtedness of the
Company.
 
     The specific designation, number of Preferred Securities, dividend rate (or
method of determination thereof), and any other rights, preferences, privileges,
limitations and restrictions relating to the Preferred Securities of the
particular series in respect of which this Prospectus is being delivered will be
set forth in a Prospectus Supplement pertaining to such series.
 
     The Preferred Securities may be offered in amounts, at prices and on terms
to be determined at the time of offering; provided, however, that the aggregate
initial public offering price of all Preferred Securities offered hereby shall
not exceed $100,000,000.
                               ------------------
 
THESE SECURITIES HAVE NOT BEEN APPROVED OR DISAPPROVED BY THE SECURITIES AND
  EXCHANGE COMMISSION OR ANY STATE SECURITIES COMMISSION NOR HAS THE
     SECURITIES AND EXCHANGE COMMISSION OR ANY STATE SECURITIES COMMISSION
      PASSED UPON THE ACCURACY OR ADEQUACY OF THIS PROSPECTUS. ANY
        REPRESENTATION TO THE CONTRARY IS A CRIMINAL OFFENSE.
                               ------------------
 
     The Preferred Securities may be sold to or through underwriters or dealers
as designated from time to time. See "Plan of Distribution." The names of any
such underwriters or dealers involved in the sale of the Preferred Securities of
the particular series in respect of which this Prospectus is being delivered,
the number of Preferred Securities to be purchased by any such underwriters or
dealers and any applicable commissions or discounts will be set forth in the
Prospectus Supplement. The net proceeds to the Company will also be set forth in
the Prospectus Supplement.
                               ------------------
 
               The date of this Prospectus is September 13, 1994.
   27
 
                             AVAILABLE INFORMATION
 
         The Company is subject to the informational requirements of the
Securities Exchange Act of 1934, as amended (the "Exchange Act"), and in
accordance therewith files reports, proxy statements and other information with
the Securities and Exchange Commission (the "Commission"). Reports, proxy
statements and other information filed by the Company with the Commission may be
inspected and copied at the public reference facilities maintained by the
Commission at Room 1024, 450 Fifth Street, N.W., Washington, D.C. 20549, and at
the Commission's Regional Offices located at Suite 1400, Northwestern Atrium
Center, 500 West Madison Street, Chicago, Illinois 60661 and at 13th Floor,
Seven World Trade Center, New York, New York 10048. Copies of such material may
be obtained from the public reference section of the Commission, 450 Fifth
Street, N.W., Washington, D.C. 20549, at prescribed rates. Such reports, proxy
statements and other information concerning the Company may also be inspected at
the offices of the New York Stock Exchange, 20 Broad Street, New York, New York
10005 and the Chicago Stock Exchange, 440 South LaSalle Street, Chicago,
Illinois 60605, on which exchanges certain of the Company's securities are
listed. In addition, such reports, proxy statements and other information
concerning the Company can be inspected at the principal office of the Company,
500 South 27th Street, Decatur, Illinois 62525.
 
     This Prospectus does not contain all the information set forth in the
Registration Statement on Form S-3 (together with all amendments and exhibits
thereto, the "Registration Statement"), which the Company and Illinois Power
Capital have filed with the Commission under the Securities Act of 1933, as
amended (the "Securities Act"). Statements contained or incorporated by
reference herein concerning the provisions of documents are necessarily
summaries of such documents, and each statement is qualified in its entirety by
reference to the Registration Statement.
 
     No separate financial statements of Illinois Power Capital have been
included herein. The Company and Illinois Power Capital do not consider that
such financial statements would be material to holders of Preferred Securities
because Illinois Power Capital is a newly formed special purpose entity, has no
operating history and no independent operations and is not engaged in, and does
not propose to engage in, any activity other than as set forth below. See
"Illinois Power Capital."
 
                INCORPORATION OF CERTAIN DOCUMENTS BY REFERENCE
 
     The following documents heretofore filed by the Company with the Commission
pursuant to the Exchange Act are incorporated herein by reference:
 
          1. The Company's Annual Report on Form 10-K for the year ended
     December 31, 1993;
 
          2. The Company's Current Reports on Form 8-K dated February 9, 1994
     and May 27, 1994; and
 
          3. The Company's Quarterly Reports on Form 10-Q for the quarters ended
     March 31, 1994 and June 30, 1994.
 
     All documents subsequently filed by the Company pursuant to Sections 13(a),
13(c), 14 or 15(d) of the Exchange Act after the date of this Prospectus and
prior to the termination of the offering of the Preferred Securities offered
hereby, shall be deemed to be incorporated by reference in this Prospectus and
to be a part hereof from the date of filing of such documents. Any statement
contained in a document incorporated or deemed to be incorporated by reference
herein shall be deemed to be modified or superseded for purposes of this
Prospectus to the extent that a statement contained herein or in any other
subsequently filed document which also is or is deemed to be incorporated by
reference herein or in the Prospectus Supplement modifies or supersedes such
statement. Any such statement so modified or superseded shall not be deemed,
except as so modified or superseded, to constitute a part of this Prospectus.
 
         THE COMPANY WILL PROVIDE WITHOUT CHARGE TO EACH PERSON TO WHOM A COPY
OF THIS PROSPECTUS HAS BEEN DELIVERED, ON THE WRITTEN OR ORAL REQUEST OF SUCH
PERSON, A COPY OF ANY OR ALL OF THE DOCUMENTS REFERRED TO ABOVE WHICH HAVE BEEN
OR MAY BE INCORPORATED IN THIS PROSPECTUS BY REFERENCE, OTHER THAN EXHIBITS TO
SUCH DOCUMENTS WHICH ARE NOT SPECIFICALLY INCORPORATED BY REFERENCE INTO THE
INFORMATION THAT THE PROSPECTUS INCORPORATES. REQUESTS FOR SUCH COPIES SHOULD BE
DIRECTED TO MR. ALEC G. DREYER, CONTROLLER, ILLINOIS POWER COMPANY, 500 SOUTH
27TH STREET, DECATUR, ILLINOIS 62525, TELEPHONE NUMBER: (217) 424-6600.
 
                                        2
   28
 
                             ILLINOIS POWER COMPANY
 
     The Company was incorporated under the laws of the State of Illinois on May
25, 1923. Effective May 27, 1994, the Company became a subsidiary of Illinova
Corporation, an exempt holding company under the Public Utility Holding Company
Act of 1935, as amended, pursuant to a merger in which each outstanding share of
the Company's Common Stock was converted into one share of common stock of
Illinova Corporation. The Company is engaged in the generation, transmission,
distribution and sale of electric energy and the distribution and sale of
natural gas in the State of Illinois. Its service area is a widely diversified
industrial and agricultural area comprising approximately 15,000 square miles in
northern, central and southern Illinois. Electric service is provided at retail
to 309 incorporated municipalities, adjacent suburban and rural areas and
numerous unincorporated municipalities having an aggregate population of
approximately 1,283,000. Gas service is provided to 257 incorporated
municipalities, adjacent suburban areas and numerous unincorporated
municipalities having an aggregate population of approximately 935,000. The
larger cities served include Decatur, East St. Louis (gas only), Champaign,
Danville, Belleville, Granite City, Bloomington (electric only), Galesburg,
Urbana and Normal (electric only). The executive offices of the Company are
located at 500 South 27th Street, Decatur, Illinois 62525, and the Company's
telephone number is (217) 424-6600.
 
                             ILLINOIS POWER CAPITAL
 
     Illinois Power Capital is a limited partnership formed under the Delaware
Revised Uniform Limited Partnership Act, as amended (the "Partnership Act").
Illinois Power Capital exists for the sole purpose of issuing its partner
interests and using the proceeds thereof to purchase certain debt securities of
the Company. The Company is the sole general partner (the "General Partner") of
Illinois Power Capital and will manage all of the business and affairs of
Illinois Power Capital. Holders of Preferred Securities will be limited partners
of Illinois Power Capital. The Company, as the General Partner of Illinois Power
Capital, will make capital contributions to Illinois Power Capital from time to
time to the extent required so that the total contributions made by the General
Partner shall at all times be at least equal to 3% of the total contributions
made by all partners. The rights and obligations of the General Partner and the
limited partners of Illinois Power Capital will be governed by the Partnership
Act and by an Amended and Restated Agreement of Limited Partnership of Illinois
Power Capital (the "Partnership Agreement") substantially in the form filed as
an exhibit to the Registration Statement of which this Prospectus and the
accompanying Prospectus Supplement form a part.
 
     Illinois Power Capital's principal place of business and registered office
in the State of Delaware is c/o The Corporation Trust Company, Corporation Trust
Center, 1209 Orange Street, Wilmington, New Castle County, Delaware 19801,
telephone: (302) 658-7581.
 
                                USE OF PROCEEDS
 
     The proceeds to be received by Illinois Power Capital from the sale of the
Preferred Securities will be used to purchase Subordinated Debentures of the
Company and, unless otherwise specified in any Prospectus Supplement, will be
applied by the Company to the payment or provision for payment at maturity, or
the purchase or the redemption prior to maturity of outstanding securities of
the Company, and for general corporate purposes.
 
                                        3
   29
 
          RATIO OF EARNINGS TO FIXED CHARGES AND RATIO OF EARNINGS TO
        COMBINED FIXED CHARGES AND PREFERRED STOCK DIVIDEND REQUIREMENTS
 


                                            YEAR ENDED DECEMBER 31,                      12 MONTHS
                                ------------------------------------------------           ENDED
                                1989        1990       1991     1992     1993(A)      JUNE 30, 1994(A)
                                -----       ----       ----     ----     -------      ----------------
                                                                    
Ratio of Earnings to Fixed
  Charges(b)..................  (0.52)(c)   0.70(c)    1.85     2.02       0.80(c)          0.93(c)
Ratio of Earnings to Combined
  Fixed Charges and Preferred
  Stock Dividend
  Requirements(b).............  (0.45)(d)   0.60(d)    1.48     1.61       0.70(d)          0.82(d)

 
- ---------------
 
(a) Subsequent to the Company's merger with Illinova Corporation, net assets of
     Illinova Generating Company (formerly IP Group, Inc.) were transferred in
     the form of a dividend from the Company to Illinova Corporation. The
     information contained herein has been restated to reflect the financial
     results of the Company's current operations.
 
(b) Earnings used in the calculation of the ratio of earnings to fixed charges
     and the ratio of earnings to combined fixed charges and preferred stock
     dividend requirements include the allowance for funds used during
     construction and the deferred financing costs associated with the Company's
     Clinton Power Station, and are before deduction of income taxes and fixed
     charges. Fixed charges include interest on long-term debt, related
     amortization of debt discount, premium, and expense, other interest and
     that portion of rent expense which is estimated to be representative of the
     interest component. Preferred stock dividend requirements have been
     increased to an amount representing the pre-tax earnings required to cover
     such dividend requirements.
 
(c) The ratios of earnings to fixed charges for the twelve months ended June 30,
     1994 and for the years ended December 31, 1993, 1990 and 1989 of 0.93,
     0.80, 0.70 and (0.52), respectively, indicate that earnings were inadequate
     to cover fixed charges. The dollar amounts of the coverage deficiency for
     the twelve months ended June 30, 1994, and for the years ended 1993, 1990
     and 1989 were approximately $13 million, $37 million, $68 million and $375
     million, respectively. Excluding the loss on disallowed plant costs of $200
     million, net of income taxes, recorded in the third quarter of 1993, the
     ratio of earnings to fixed charges would have been 2.42 for the twelve
     months ended June 30, 1994 and 2.25 for the year ended 1993. Excluding the
     loss on disallowed plant costs of $137 million, net of income taxes,
     recorded in the fourth quarter of 1990, the ratio of earnings to fixed
     charges would have been 1.41 for the year ended 1990. Excluding the loss on
     disallowed plant costs of $346 million, net of income taxes, recorded in
     the first quarter of 1989, the ratio of earnings to fixed charges would
     have been 1.31 for the year ended 1989.
 
(d) The ratios of earnings to combined fixed charges and preferred stock
     dividend requirements for the twelve months ended June 30, 1994 and for the
     years ended December 31, 1993, 1990 and 1989 of 0.82, 0.70, 0.60 and
     (0.45), respectively, indicate that earnings were inadequate to cover
     combined fixed charges and preferred stock dividend requirements. The
     dollar amounts of the coverage deficiency for the twelve months ended June
     30, 1994, and for the years ended 1993, 1990 and 1989 were approximately
     $38 million, $63 million, $105 million and $412 million, respectively.
     Excluding the loss on disallowed plant costs of $200 million, net of income
     taxes, recorded in the third quarter of 1993, the ratio of earnings to
     combined fixed charges and preferred stock dividend requirements would have
     been 1.98 for the twelve months ended June 30, 1994 and 1.83 for the year
     ended 1993. Excluding the loss on disallowed plant costs of $137 million,
     net of income taxes, recorded in the fourth quarter of 1990, the ratio of
     earnings to combined fixed charges and preferred stock dividend
     requirements would have been 1.09 for the year ended 1990. Excluding the
     loss on disallowed plant costs of $346 million, net of income taxes,
     recorded in the first quarter of 1989, the ratio of earnings to combined
     fixed charges and preferred stock dividend requirements would have been
     1.06 for the year ended 1989.
 
                                        4
   30
 
                    DESCRIPTION OF THE PREFERRED SECURITIES
 
     Illinois Power Capital may issue, from time to time, Preferred Securities,
in one or more series, having terms described in the Prospectus Supplement
relating thereto. The limited partnership agreement of Illinois Power Capital
will be amended and restated (as so amended and restated, the "Partnership
Agreement") to authorize the establishment of one or more series of Preferred
Securities, having such terms, including dividends, redemption, voting,
liquidation rights and such other preferred, deferred or other special rights or
such restrictions as shall be set forth therein or otherwise established by the
General Partner pursuant thereto. Reference is made to the Prospectus Supplement
relating to the Preferred Securities of a particular series for specific terms,
including (i) the distinctive designation of such series which shall distinguish
it from other series; (ii) the number of Preferred Securities included in such
series, which number may be increased or decreased from time to time unless
otherwise provided by the General Partner in creating the series; (iii) the
annual dividend rate (or method of determining such rate) for Preferred
Securities of such series and the date or dates upon which such dividends shall
be payable; provided, however, dividends on any series of Preferred Securities
shall be payable on a monthly basis to holders of such series of Preferred
Securities as of a record date in each month during which such series of
Preferred Securities are outstanding; (iv) whether dividends on Preferred
Securities of such series shall be cumulative, and, in the case of Preferred
Securities of any series having cumulative dividend rights, the date or dates or
method of determining the date or dates from which dividends on Preferred
Securities of such series shall be cumulative; (v) the amount or amounts which
shall be paid out of the assets of Illinois Power Capital to the holders of
Preferred Securities of such series upon voluntary or involuntary dissolution,
winding-up or termination of Illinois Power Capital; (vi) the price or prices at
which, the period or periods within which and the terms and conditions upon
which Preferred Securities of such series may be redeemed or purchased, in whole
or in part, at the option of Illinois Power Capital or the General Partner;
(vii) the obligation, if any, of Illinois Power Capital to purchase or redeem
Preferred Securities of such series and the price or prices at which, the period
or periods within which and the terms and conditions upon which Preferred
Securities of such series shall be purchased or redeemed, in whole or in part,
pursuant to such obligation; (viii) the voting rights, if any, of Preferred
Securities of such series in addition to those required by law, including the
number of votes per Preferred Security and any requirement for the approval by
the holders of Preferred Securities, or of Preferred Securities of one or more
series, or of both, as a condition to specified action or amendments to the
Partnership Agreement; and (ix) any other relative rights, preferences,
privileges, limitations or restrictions of Preferred Securities of the series
not inconsistent with the Partnership Agreement or with applicable law. All
Preferred Securities offered hereby will be guaranteed by the Company to the
extent set forth below under "Description of the Guarantee." Any applicable
federal income tax considerations applicable to any offering of Preferred
Securities will be described in the Prospectus Supplement relating thereto.
 
                          DESCRIPTION OF THE GUARANTEE
 
     Set forth below is a summary of information concerning the Guarantee which
will be executed and delivered by the Company for the benefit of the holders
from time to time of Preferred Securities. The summary does not purport to be
complete and is subject in all respects to the provisions of, and is qualified
in its entirety by reference to, the Guarantee, which is filed as an exhibit to
the Registration Statement of which this Prospectus forms a part.
 
GENERAL
 
     The Company will irrevocably and unconditionally agree, to the extent set
forth herein, to pay in full, to the holders of the Preferred Securities of each
series, the Guarantee Payments (as defined below) (except to the extent paid by
Illinois Power Capital), as and when due, regardless of any defense, right of
set-off or counterclaim which Illinois Power Capital may have or assert. The
following payments with respect to any series of Preferred Securities to the
extent not paid by Illinois Power Capital (the "Guarantee Payments") will be
subject to the Guarantee (without duplication): (i) any accumulated and unpaid
dividends which are required to be paid on the Preferred Securities of such
series, to the
 
                                        5
   31
 
extent Illinois Power Capital shall have sufficient cash on hand to permit such
payment and funds legally available therefor, (ii) the redemption price,
including all accumulated and unpaid dividends (the "Redemption Price"), payable
with respect to any Preferred Securities called for redemption by Illinois Power
Capital to the extent Illinois Power Capital shall have sufficient cash on hand
to permit such payment and funds legally available therefor, and (iii) upon a
liquidation of Illinois Power Capital, the lesser of (a) the aggregate of the
liquidation preference and all accumulated and unpaid dividends on the Preferred
Securities of such series to the date of payment and (b) the amount of assets of
Illinois Power Capital remaining available for distribution to holders of
Preferred Securities of such series in liquidation of Illinois Power Capital.
The Company's obligation to make a Guarantee Payment may be satisfied by direct
payment of the required amounts by the Company to the holders of Preferred
Securities or by causing Illinois Power Capital to pay such amounts to such
holders.
 
CERTAIN COVENANTS OF THE COMPANY
 
     In the Guarantee, the Company will covenant that, so long as any Preferred
Securities remain outstanding, the Company will not declare or pay any dividend
on, or redeem, purchase, acquire or make a liquidation payment with respect to,
any of its capital stock or make any guarantee payment with respect to the
foregoing if at such time the Company shall be in default with respect to its
payment or other obligations under the Guarantee or there shall have occurred
and is continuing any event that would constitute an Event of Default under the
Indenture.
 
AMENDMENTS AND ASSIGNMENT
 
     Except with respect to any changes which do not adversely affect the rights
of holders of Preferred Securities (in which case no vote will be required), the
Guarantee may be changed only with the prior approval of the holders of not less
than 66 2/3% in liquidation preference of the outstanding Preferred Securities
of each affected series (voting together as one class). The manner of obtaining
any such approval of holders of the Preferred Securities of each series will be
as set forth in an accompanying Prospectus Supplement. All guarantees and
agreements contained in the Guarantee shall bind the successors, assigns,
receivers, trustees and representatives of the Company and shall inure to the
benefit of the holders of the Preferred Securities then outstanding.
 
TERMINATION OF THE GUARANTEE
 
     The Guarantee will terminate and be of no further force and effect as to
the Preferred Securities of any series upon full payment of the Redemption Price
of all Preferred Securities of such series, and will terminate completely upon
full payment of the amounts payable upon liquidation of Illinois Power Capital.
The Guarantee will continue to be effective or will be reinstated, as the case
may be, if at any time any holder of Preferred Securities of any series must
restore payment of any sums paid under such series of Preferred Securities or
the Guarantee.
 
STATUS OF THE GUARANTEE
 
     The Guarantee will constitute an unsecured obligation of the Company and
will rank (i) subordinate and junior in right of payment to all liabilities of
the Company, (ii) pari passu with the most senior preferred or preference stock
now or hereafter issued by the Company and with any guarantee now or hereafter
entered into by the Company in respect of any preferred or preference stock of
any affiliate of the Company and (iii) senior to the Company's Common Stock. The
Partnership Agreement provides that each holder of Preferred Securities by
acceptance thereof agrees to the subordination provisions and other terms of the
Guarantee.
 
     The Guarantee will constitute a guarantee of payment and not of collection.
The Guarantee will be deposited with the General Partner to be held for the
benefit of the holders of each series of the Preferred Securities. In the event
of the appointment of a Special Representative to, among other things, enforce
the Guarantee, the Special Representative may take possession of the Guarantee
for such purpose. If no
 
                                        6
   32
Special Representative has been appointed to enforce the Guarantee, the General
Partner has the right to enforce the Guarantee on behalf of the holders of each
series of the Preferred Securities. The holders of not less than 10% in
aggregate liquidation preference of the Preferred Securities have the right to
direct the time, method and place of conducting any proceeding for any remedy
available in respect of the Guarantee, including the giving of directions to the
General Partner or the Special Representative, as the case may be. If the
General Partner or the Special Representative fails to enforce the Guarantee as
above provided, any holder of Preferred Securities may institute a legal
proceeding directly against the Company to enforce its rights under the
Guarantee, without first instituting a legal proceeding against Illinois Power
Capital or any other person or entity. The Guarantee will not be discharged
except by payment of the Guarantee Payments in full to the extent not paid by
Illinois Power Capital and by complete performance of all obligations under the
Guarantee.
 
GOVERNING LAW
 
     The Guarantee will be governed by and construed in accordance with the laws
of the State of Illinois.
 
                   DESCRIPTION OF THE SUBORDINATED DEBENTURES
 
     Subordinated Debentures may be issued from time to time in one or more
series under an Indenture, (the "Indenture"), between the Company and The First
National Bank of Chicago, as Trustee (the "Trustee"). The following summary does
not purport to be complete and is subject in all respects to the provisions of,
and is qualified in its entirety by reference to, the Indenture, which is filed
as an exhibit to the Registration Statement of which this Prospectus forms a
part. Whenever particular provisions or defined terms in the Indenture are
referred to herein, such provisions or defined terms are incorporated by
reference herein. Section and Article references used herein are references to
provisions of the Indenture unless otherwise noted.
 
GENERAL
 
     The Subordinated Debentures will be unsecured, subordinated obligations of
the Company. The Indenture does not limit the aggregate principal amount of
Subordinated Debentures which may be issued thereunder and provides that the
Subordinated Debentures may be issued thereunder from time to time in one or
more series.
 
     The Subordinated Debentures are issuable in one or more series pursuant to
an indenture supplemental to the Indenture or a resolution of the Company's
Board of Directors or an authorized committee thereof (each, a "Supplemental
Indenture"). The aggregate principal amount of Subordinated Debentures relating
to Preferred Securities of any series will be set forth in the Prospectus
Supplement for such series and will be equal to the sum of the aggregate
liquidation preference of the Preferred Securities for such series and the
General Partner's capital contribution with respect to the Preferred Securities
for such series. Subordinated Debentures relating to Preferred Securities of any
series subsequently may be distributed pro rata to holders of Preferred
Securities of such series in connection with the dissolution of Illinois Power
Capital upon the occurrence of certain events described in the Prospectus
Supplement relating to the Preferred Securities of such series.
 
     The Restated Articles of Incorporation, as amended, of the Company limit
the amount of unsecured indebtedness that the Company may issue or assume,
without the consent of the holders of a majority of the total number of shares
of preferred stock then outstanding, to 20% of the aggregate of the total
principal amount of all outstanding bonds or other securities representing
secured indebtedness of the Company and the capital and surplus of the Company
as then stated on the Company's books. At July 31, 1994, the Company could have
issued approximately $210 million of unsecured indebtedness (such as the
Subordinated Debentures) without violating this provision.
 
     Reference is made to the Prospectus Supplement which will accompany this
Prospectus for the following terms of the series of Subordinated Debentures
being offered thereby: (i) the specific title of
 
                                        7
   33
 
such Subordinated Debentures; (ii) any limit on the aggregate principal amount
of such Subordinated Debentures; (iii) the date or dates on which the principal
of such Subordinated Debentures is payable or the method of determination of
such date or dates; (iv) the rate or rates at which such Subordinated Debentures
will bear interest or the method of determination of such rate or rates
(including the rates at which overdue principal shall bear interest, if
different, and, if applicable, the rate or rates at which overdue premium or
interest shall bear interest, if any); (v) the date or dates from which such
interest shall accrue, the interest payment dates on which such interest will be
payable or the manner of determination of such interest payment dates and the
record dates for the determination of holders to whom interest is payable on any
such interest payment dates; (vi) the right, if any, to extend the interest
payment periods and the maximum duration of any such extension; (vii) the period
or periods within which, the price or prices at which and the terms and
conditions upon which such Subordinated Debentures may be redeemed, in whole or
in part, at the option of the Company; (viii) the obligation, if any, of the
Company to redeem or purchase such Subordinated Debentures pursuant to any
sinking fund or analogous provisions or at the option of the holder thereof and
the period or periods, the price or prices at which, and the terms and
conditions upon which, such Subordinated Debentures shall be redeemed or
purchased, in whole or part, pursuant to such obligation; (ix) the form of such
Subordinated Debentures; (x) if other than denominations of $25 or any integral
multiple thereof, the denominations in which such Subordinated Debentures shall
be issuable; (xi) any and all other terms with respect to such series; and (xii)
whether such Subordinated Debentures are issuable as a global security, and in
such case, the identity of the depository.
 
     The Indenture does not contain any provisions that afford holders of
Subordinated Debentures protection in the event of a highly leveraged
transaction involving the Company.
 
SUBORDINATION
 
     The Indenture provides that the Subordinated Debentures are subordinate and
junior in right of payment to all Senior Indebtedness (as defined below) of the
Company as provided in the Indenture. No payment of principal of (including
redemption and sinking fund payments), premium, if any, or interest on, the
Subordinated Debentures may be made if any Senior Indebtedness is not paid when
due, any applicable grace period with respect to such default has ended and such
default has not been cured or waived or has ceased to exist, or if the maturity
of any Senior Indebtedness has been accelerated because of a default. Upon any
distribution of assets of the Company to creditors upon any dissolution,
winding-up, liquidation or reorganization, whether voluntary or involuntary or
in bankruptcy, insolvency, receivership or other proceedings, all principal of,
and premium, if any, and interest due or to become due on, all Senior
Indebtedness must be paid in full before the holders of the Subordinated
Debentures are entitled to receive or retain any payment. The rights of the
holders of the Subordinated Debentures will be subrogated to the rights of the
holders of Senior Indebtedness to receive payments or distributions applicable
to Senior Indebtedness until all amounts owing on the Subordinated Debentures
are paid in full.
 
     The term "Senior Indebtedness" shall mean the principal of, premium, if
any, interest on and any other payment due pursuant to any of the following,
whether outstanding at the date of execution of the Indenture or thereafter
incurred, created or assumed:
 
          (a) all indebtedness of the Company (other than non-recourse
     indebtedness and indebtedness issued under the Indenture) evidenced by
     notes, debentures, bonds or other securities sold by the Company for money;
 
          (b) all indebtedness of others of the kinds described in the preceding
     clause (a) assumed by or guaranteed in any manner by the Company (other
     than the Guarantee) or in effect guaranteed by the Company by an agreement
     to purchase, contingent or otherwise; and
 
          (c) all renewals, extensions or refundings of indebtedness of the
     kinds described in either of the preceding clauses (a) and (b) unless, in
     the case of any particular indebtedness, renewal, extension or refunding,
     the instrument creating or evidencing the same or the assumption or
 
                                        8
   34
 
     guarantee of the same expressly provides that such indebtedness, renewal,
     extension or refunding is not superior in right of payment to or is pari
     passu with the Subordinated Debentures.
 
Such Senior Indebtedness shall continue to be Senior Indebtedness and to be
entitled to the benefits of the subordination provisions irrespective of any
amendment, modification or waiver of any term of such Senior Indebtedness.
 
     The Indenture does not limit the aggregate amount of Senior Indebtedness
which may be issued. As of June 30, 1994, Senior Indebtedness of the Company
aggregated approximately $2.2 billion.
 
CERTAIN COVENANTS OF THE COMPANY
 
     The Company will covenant that it will not declare or pay any dividend on,
or redeem, purchase, acquire or make a distribution or liquidation payment with
respect to, any of its capital stock, if at such time (i) there shall have
occurred and be continuing any event that would constitute an Event of Default
under any Indenture, (ii) the Company shall be in default with respect to its
payment or any obligations under the Guarantee or (iii) the Company shall have
given notice of its selection of an extended interest payment period as provided
in the Indenture and such period, or any extension thereof, shall be continuing.
The Company will also covenant (i) to remain the sole general partner of
Illinois Power Capital and maintain 100% ownership of the general partner
interests thereof; provided, that any permitted successor of the Company under
the Indenture may succeed to the Company's duties as General Partner, (ii) to
contribute capital to the extent required to maintain its capital at an amount
equal to at least 3% of the total capital contributions to Illinois Power
Capital, (iii) not to voluntarily dissolve, wind-up or terminate Illinois Power
Capital, except in connection with the distribution of Subordinated Debentures
to the holders of Preferred Securities in liquidation of Illinois Power Capital
and in connection with certain mergers, consolidations or amalgamations
permitted by the Partnership Agreement, (iv) to timely perform all of its duties
as the general partner in Illinois Power Capital (including the duty to pay
dividends on the Preferred Securities) and (v) to use its reasonable efforts to
cause Illinois Power Capital to remain a limited partnership except in
connection with a distribution of Subordinated Debentures and in connection with
certain mergers, consolidations or amalgamations permitted by the Partnership
Agreement, and otherwise continue to be treated as a partnership for United
States federal income tax purposes except in connection with a distribution of
Subordinated Debentures.
 
FORM, EXCHANGE, REGISTRATION AND TRANSFER
 
     Subordinated Debentures of each series will be issued in registered form
and either will be in certificated form or will be represented by one or more
global securities. If not represented by one or more global securities,
Subordinated Debentures may be presented for registration of transfer (with the
form of transfer endorsed thereon duly executed) or exchange, at the office of
the Debenture Registrar, without service charge and upon payment of any taxes
and other governmental charges. Such transfer or exchange will be effected upon
the Company or the Debenture Registrar being satisfied with the documents of
title and identity of the person making the request. The Company has appointed
the Trustee as Debenture Registrar with respect to the Subordinated Debentures.
 
     The Company shall not be required to (i) issue, register the transfer of or
exchange any Subordinated Debenture during a period beginning at the opening of
business 15 days before any mailing of Notice of Redemption of less than all the
outstanding Subordinated Debentures of the series of which such Subordinated
Debenture is a part, and ending at the close of business on the day of such
mailing or (ii) register the transfer of or exchange any Subordinated Debentures
called for redemption.
 
PAYMENT AND PAYING AGENTS
 
     Payment of principal of and premium, if any, on any Subordinated Debenture
will be made only against surrender to the Paying Agent of such Subordinated
Debenture. Principal of and any premium and interest, if any, on Subordinated
Debentures will be payable, subject to any applicable laws and regulations, at
the office of such Paying Agent or Paying Agents as the Company may designate
from
 
                                        9
   35
 
time to time, except that at the option of the Company payment of any interest
may be made by check mailed to the address of the person entitled thereto as
such address shall appear in the Debenture Register with respect to such
Subordinated Debentures. Payment of interest on a Subordinated Debenture on any
Interest Payment Date will be made to the person in whose name such Subordinated
Debenture (or Predecessor Security) is registered at the close of business on
the Regular Record Date for such interest payment.
 
     The Company will act as Paying Agent with respect to the Subordinated
Debentures. The Company may at any time designate additional Paying Agents or
rescind the designation of any Paying Agents or approve a change in the office
through which any Paying Agent acts, except that the Company will be required to
maintain a Paying Agent in each Place of Payment for each series of the
respective Subordinated Debentures.
 
     All moneys paid by the Company to a Paying Agent for the payment of the
principal of or premium or interest, if any, on any Subordinated Debenture of
any series which remain unclaimed at the end of two years after such principal,
premium, if any, or interest shall have become due and payable will be repaid to
the Company and the holder of such Subordinated Debenture will thereafter look
only to the Company for payment thereof.
 
GLOBAL DEBENTURES
 
     If any Subordinated Debentures of a series are represented by one or more
global securities, the applicable Prospectus Supplement will describe the
circumstances, if any, under which beneficial owners of interests in any such
Global Debenture may exchange such interests for Subordinated Debentures of such
series and of like tenor and principal amount in any authorized form and
denomination. Principal of and any premium and interest on a Global Debenture
will be payable in the manner described in the applicable Prospectus Supplement.
 
     The specific terms of the depository arrangement with respect to any
portion of a series of Subordinated Debentures to be represented by a Global
Debenture will be described in the applicable Prospectus Supplement.
 
MODIFICATION OF THE INDENTURE
 
     The Indenture contains provisions permitting the Company and the Trustee,
with consent of the holders of not less than a majority in principal amount of
the Subordinated Debentures of each series which are affected by the
modification, to modify the Indenture or any Supplemental Indenture affecting
that series or the rights of the holders of that series of Subordinated
Debentures; provided, that no such modification may, without the consent of the
holder of each outstanding Subordinated Debenture affected thereby, (i) extend
the fixed maturity of any Subordinated Debentures of any series, or reduce the
principal amount thereof, or reduce the rate or extend the time of payment of
interest thereon, or reduce any premium payable upon the redemption thereof,
without the consent of the holder of each Subordinated Debenture so affected or
(ii) reduce the percentage of Subordinated Debentures, the holders of which are
required to consent to any such supplemental indenture, without the consent of
the holders of each Subordinated Debenture then outstanding and affected
thereby.
 
     In addition, the Company and the Trustee may execute, without the consent
of any holder of Subordinated Debentures, any Supplemental Indenture for certain
other usual purposes including the creation of any new series of Subordinated
Debentures.
 
                                       10
   36
 
EVENTS OF DEFAULT
 
     The Indenture provides that any one or more of the following described
events, which has occurred and is continuing, constitutes an "Event of Default"
with respect to each series of Subordinated Debentures:
 
          (a) failure for 10 days to pay interest on the Subordinated Debentures
     of that series, including any Additional Interest in respect thereof, when
     due, provided that a valid extension of an interest payment period by the
     Company in accordance with a Supplemental Indenture shall not constitute a
     failure to pay interest for this purpose; or
 
          (b) failure to pay principal or premium, if any, on the Subordinated
     Debentures of that series when due, whether at maturity, upon redemption by
     declaration or otherwise, or to make any sinking fund payment with respect
     to that series; or
 
          (c) failure to observe or perform any other covenant (other than those
     specifically relating to another series) contained in the Indenture for 90
     days after notice; or
 
          (d) the dissolution, winding-up or termination of Illinois Power
     Capital, except in connection with the distribution of Subordinated
     Debentures to the holders of Preferred Securities in liquidation of
     Illinois Power Capital and in connection with certain mergers,
     consolidations or amalgamations permitted by the Partnership Agreement; or
 
          (e) certain events in bankruptcy, insolvency or reorganization of the
     Company or Illinois Power Capital.
 
     The holders of a majority in aggregate outstanding principal amount of any
series of the Subordinated Debentures have the right to direct the time, method
and place of conducting any proceeding for any remedy available to the Trustee
for that series. The Trustee or the holders of not less than 25% in aggregate
outstanding principal amount of any particular series of the Subordinated
Debentures (unless the principal of all of the Subordinated Debentures of that
series has been declared due and payable) may declare the principal due and
payable immediately on default with respect to such series, but the holders of a
majority in aggregate outstanding principal amount of such series may annul such
declaration and waive the default if the default has been cured and a sum
sufficient to pay all matured installments of interest and principal and any
premium has been deposited with the Trustee.
 
     The holders of a majority in aggregate outstanding principal amount of all
series of the Subordinated Debentures affected thereby may, on behalf of the
holders of all of the Subordinated Debentures of such series, waive any past
default, except a default in the payment of principal, premium, if any, or
interest. The Company is required to file annually with the Trustee a
certificate as to whether or not the Company is in compliance with all the
conditions and covenants under the Indenture.
 
CONSOLIDATION, MERGER AND SALE
 
     The Indenture does not contain any covenant which restricts the Company's
ability to merge or consolidate with or into any other corporation, sell or
convey all or substantially all of its assets to any person, firm or corporation
or otherwise engage in restructuring transactions.
 
DEFEASANCE AND DISCHARGE
 
     Under the terms of the Indenture, the Company will be discharged from any
and all obligations in respect of the Subordinated Debentures of any series
(except in each case for certain obligations to register the transfer or
exchange of Subordinated Debentures, replace stolen, lost or mutilated
Subordinated Debentures, maintain paying agencies and hold moneys for payment in
trust) if the Company deposits with the Trustee, in trust, moneys or Government
Obligations, in an amount sufficient to pay all the principal of, and interest
on, the Subordinated Debentures of such series on the dates such payments are
due in accordance with the terms of such Subordinated Debentures.
 
                                       11
   37
 
GOVERNING LAW
 
     The Indenture and the Subordinated Debentures will be governed by, and
construed in accordance with, the laws of the State of New York.
 
INFORMATION CONCERNING THE TRUSTEE
 
     The Trustee shall have and be subject to all the duties and
responsibilities specified with respect to an indenture trustee under the Trust
Indenture Act. Subject to such provision, the Trustee is under no obligation to
exercise any of the powers vested in it by the Indenture at the request of any
holder of Subordinated Debentures, unless offered reasonable indemnity by such
holder against the costs, expenses and liabilities which might be incurred
thereby. The Trustee is not required to expand or risk its own funds or
otherwise incur personal financial liability in the performance of its duties if
the Trustee reasonably believes that repayment or adequate indemnity is not
reasonably assured to it.
 
     The Company maintains a deposit account and banking relationship with the
Trustee.
 
MISCELLANEOUS
 
     The Company will have the right at all times to assign any of its rights or
obligations under the Indenture to a direct or indirect wholly-owned subsidiary
of the Company; provided, that, in the event of any such assignment, the Company
will remain liable for all such obligations. Subject to the foregoing, the
Indenture will be binding upon and inure to the benefit of the parties thereto
and their respective successors and assigns. The Indenture provides that it may
not otherwise be assigned by the parties thereto.
 
                              PLAN OF DISTRIBUTION
 
     Illinois Power Capital may offer or sell Preferred Securities to one or
more underwriters for public offering and sale by them. Illinois Power Capital
may sell Preferred Securities as soon as practicable after effectiveness of the
Registration Statement, provided that favorable market conditions exist. Any
such underwriter involved in the offer and sale of the Preferred Securities will
be named in an applicable Prospectus Supplement.
 
     Underwriters may offer and sell the Preferred Securities at a fixed price
or prices, which may be changed, or from time to time at market prices
prevailing at the time of sale, at prices related to such prevailing market
prices or at negotiated prices. In connection with the sale of Preferred
Securities, underwriters may be deemed to have received compensation from the
Company and/or Illinois Power Capital in the form of underwriting discounts or
commissions. Underwriters may sell Preferred Securities to or through dealers,
and such dealers may receive compensation in the form of discounts, concessions
or commissions from the underwriters.
 
     Any underwriting compensation paid by the Company and/or Illinois Power
Capital to underwriters in connection with the offering of Preferred Securities,
and any discounts, concessions or commissions allowed by underwriters to
participating dealers, will be set forth in an applicable Prospectus Supplement.
Underwriters and dealers participating in the distribution of the Preferred
Securities may be deemed to be underwriters, and any discounts and commissions
received by them and any profit realized by them on resale of the Preferred
Securities may be deemed to be underwriting discounts and commissions, under the
Securities Act. Underwriters and dealers may be entitled, under agreement with
the Company or Illinois Power Capital, to indemnification against and
contribution toward certain civil liabilities, including liabilities under the
Securities Act, and to reimbursement by the Company and/or Illinois Power
Capital for certain expenses.
 
     Underwriters and dealers may engage in transactions with, or perform
services for, the Company and/or Illinois Power Capital and/or any of their
affiliates in the ordinary course of business.
 
                                       12
   38
 
     Each series of Preferred Securities will be a new issue of securities and
will have no established trading market. Any underwriters to whom Preferred
Securities are sold by Illinois Power Capital for public offering and sale may
make a market in such Preferred Securities, but such underwriters will not be
obligated to do so and may discontinue any market making at any time without
notice. The Preferred Securities may or may not be listed on a national
securities exchange. No assurance can be given as to the liquidity of or the
trading markets for any Preferred Securities.
 
                                 LEGAL OPINIONS
 
     Certain legal matters will be passed upon for the Company and Illinois
Power Capital by Schiff Hardin & Waite, Chicago, Illinois, and for any
underwriters by Reid & Priest, New York, New York. Certain matters of Delaware
law relating to the validity of the Preferred Securities will be passed upon by
Richards, Layton & Finger, P.A., Wilmington, Delaware, special Delaware counsel
to the Company and Illinois Power Capital. Schiff Hardin & Waite and Reid &
Priest may rely on the opinion of Richards, Layton & Finger, P.A. as to certain
matters of Delaware law. Schiff Hardin & Waite may rely on the opinion of Reid &
Priest as to all matters of New York law, and Reid & Priest may rely on the
opinion of Schiff Hardin & Waite as to all matters of Illinois law.
 
                                    EXPERTS
 
     The financial statements incorporated in this Prospectus by reference to
the Company's Annual Report on Form 10-K for the year ended December 31, 1993
have been so incorporated in reliance on the report (which contains an
explanatory paragraph relating to the Company's change in its method of
accounting for income taxes, as discussed in Note 1 to the financial statements)
of Price Waterhouse LLP, independent accountants, given on the authority of said
firm as experts in auditing and accounting.
 
                                       13
   39
 
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     NO PERSON HAS BEEN AUTHORIZED TO GIVE ANY INFORMATION OR TO MAKE ANY
REPRESENTATIONS OTHER THAN THOSE CONTAINED IN THIS PROSPECTUS SUPPLEMENT OR THE
PROSPECTUS AND, IF GIVEN OR MADE, SUCH INFORMATION OR REPRESENTATIONS MUST NOT
BE RELIED UPON AS HAVING BEEN AUTHORIZED. THIS PROSPECTUS SUPPLEMENT AND THE
PROSPECTUS DO NOT CONSTITUTE AN OFFER TO SELL OR THE SOLICITATION OF AN OFFER TO
BUY ANY SECURITIES OTHER THAN THE SECURITIES DESCRIBED IN THIS PROSPECTUS
SUPPLEMENT AND THE PROSPECTUS OR AN OFFER TO SELL OR THE SOLICITATION OF AN
OFFER TO BUY SUCH SECURITIES IN ANY CIRCUMSTANCES IN WHICH SUCH OFFER OR
SOLICITATION IS UNLAWFUL. NEITHER THE DELIVERY OF THIS PROSPECTUS SUPPLEMENT AND
THE PROSPECTUS NOR ANY SALE MADE HEREUNDER SHALL, UNDER ANY CIRCUMSTANCES,
CREATE ANY IMPLICATION THAT THE INFORMATION HEREIN OR THEREIN IS CORRECT AS OF
ANY TIME SUBSEQUENT TO THE DATE OF SUCH INFORMATION.
                               ------------------
 
                               TABLE OF CONTENTS
 
                             PROSPECTUS SUPPLEMENT
 


                                        PAGE
                                        ----
                                     
Certain Investment Considerations....    S-3
Illinois Power Company...............    S-4
Illinois Power Capital...............    S-4
Use of Proceeds......................    S-4
Summary Financial Information of
  the Company........................    S-5
Description of the Series A Preferred
  Securities.........................    S-7
Description of the Series A
  Subordinated Debentures............   S-16
Effect of Obligations under the
  Series A Subordinated Debentures
  and the Guarantee..................   S-20
United States Taxation...............   S-20
Underwriting.........................   S-24
Legal Opinions.......................   S-25
             PROSPECTUS
Available Information................      2
Incorporation of Certain Documents by
  Reference..........................      2
Illinois Power Company...............      3
Illinois Power Capital...............      3
Use of Proceeds......................      3
Ratio of Earnings to Combined Fixed
  Charges and Preferred Stock
  Dividend Requirements..............      4
Description of the Preferred
  Securities.........................      5
Description of the Guarantee.........      5
Description of the Subordinated
  Debentures.........................      7
Plan of Distribution.................     12
Legal Opinions.......................     13
Experts..............................     13

 
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                         3,880,000 PREFERRED SECURITIES
 
                                 ILLINOIS POWER
                                    CAPITAL
 
                            GUARANTEED TO THE EXTENT
                             ILLINOIS POWER CAPITAL
                                HAS FUNDS AS SET
                                FORTH HEREIN BY
 
                                   [IP LOGO]
 
                             ILLINOIS POWER COMPANY
                                     % CUMULATIVE
                            MONTHLY INCOME PREFERRED
                              SECURITIES, SERIES A
 
                            ------------------------
 
                             PROSPECTUS SUPPLEMENT
                            ------------------------
 
                              GOLDMAN, SACHS & CO.
                            BEAR, STEARNS & CO. INC.
                           DEAN WITTER REYNOLDS INC.
                           A.G. EDWARDS & SONS, INC.
                            PAINEWEBBER INCORPORATED
                              SALOMON BROTHERS INC
                      REPRESENTATIVES OF THE UNDERWRITERS
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