Exhibit 4.1
                             ILLINOIS POWER COMPANY


                                       TO


                         HARRIS TRUST AND SAVINGS BANK,

                                   as Trustee






                             Supplemental Indenture

                            DATED AS OF JUNE 15, 1999


                                       TO


                           Mortgage and Deed of Trust

                             DATED NOVEMBER 1, 1943

                                       60


Supplemental Indenture dated as of June 15, 1999 (the "Supplemental Indenture"),
made by and between ILLINOIS POWER COMPANY, a corporation organized and existing
under  the laws of the State of  Illinois  (the  "Company"),  party of the first
part,  and HARRIS TRUST AND SAVINGS BANK, a  corporation  organized and existing
under the laws of the State of Illinois  (the  "Trustee"),  as Trustee under the
Mortgage and Deed of Trust dated November 1, 1943, hereinafter mentioned,  party
of the second part;

         WHEREAS, the Company has heretofore executed and delivered its Mortgage
and Deed of Trust dated November 1, 1943 ("Original Indenture"), to the Trustee,
for the  security of the First  Mortgage  Bonds of the Company  issued and to be
issued thereunder (the "Bonds"); and

         WHEREAS, pursuant to the terms and provisions of the Original Indenture
there were created and authorized by Supplemental Indentures thereto bearing the
following  dates,  respectively,  the First  Mortgage Bonds of the series issued
thereunder and respectively identified opposite such dates:



Date of Supplemental   Identification
    Indenture             of Series                          Called

November 1, 1943      4% Series due 1973          Bonds of the 1973 Series
                      (redeemed)

March 1, 1946         2 7/8% Series due 1976      Bonds of the 1976 Series
                      (paid at maturity)

February 1, 1948      3 1/2% Series due 1978      Bonds of the 1978 Series
                      (paid at maturity)

July 1, 1949          2 7/8% Series due 1979      Bonds of the 1979 Series
                      (paid at maturity)

April 1, 1950         2 3/4% Series due 1980      Bonds of the 1980 Series
                      (paid at maturity)

March 1, 1952         3 1/2% Series due 1982      Bonds of the 1982 Series
                      (paid at maturity)

November 1, 1953      3 1/2% Series due 1983      Bonds of the 1983 Series
                      (paid at maturity)

July 1, 1956          3 3/4% Series due 1986      Bonds of the 1986 Series
                      (paid at maturity)

May 1, 1958           4% Series due 1988          Bonds of the 1988 Series
                      (redeemed)

January 1, 1963       4 1/4% Series due 1993      Bonds of the 1993 Series
                      (paid at maturity)

October 1, 1966       5.85% Series due 1996       Bonds of the 1996 Series
                      (paid at maturity)

                                       61


Date of Supplemental  Identification
    Indenture            of Series                         Called

January 1, 1968     6 3/8% Series due 1998       Bonds of the First 1998 Series
                    (redeemed)

October 1, 1968     6 3/4% Series due October 1, Bonds of the Second 1998 Series
                    1998 (redeemed)

October 1, 1969     8.35% Series due 1999        Bonds of the First 1999 Series
                    (redeemed)

November 1, 1970    9% Series due 2000           Bonds of the 2000 Series
                    (redeemed)

October 1, 1971     7.60% Series due 2001        Bonds of the 2001 Series
                    (redeemed)

June 1, 1973        7 5/8% Series due 2003       Bonds of the First 2003 Series
                    (redeemed)

May 1, 1974         Pollution Control Series A   Bonds of the Pollution Control
                                                 Series A

September 1, 1974   10 1/2% Series due 2004      Bonds of the First 2004 Series
                    (redeemed)

July 1, 1976        8 3/4% Series due 2006       Bonds of the 2006 Series
                    (redeemed)

May 1, 1977         Pollution Control Series B   Bonds of Pollution Control
                    (redeemed)                   Series B

November 1, 1977    8 1/4% Series due 2007       Bonds of the 2007 Series
                     (redeemed)

August 1, 1978      8 7/8% Series due 2008       Bonds of the 2008 Series
                    (redeemed)

July 1, 1979        9 7/8% Series due July 1,    Bonds of the Second 2004 Series
                    2004 (redeemed)

July 31, 1980       11 3/8% Series due 1987      Bonds of the 1987 Series
                    (redeemed)

August 1, 1980      12 3/8% Series due 2010      Bonds of the 2010 Series
                    (redeemed)

July 1, 1982        14 1/2% Series due 1990      Bonds of the 1990 Series
                    (redeemed)

                                       62


Date of Supplemental   Identification
    Indenture             of Series                       Called

November 1, 1982     12% Series due 2012         Bonds of the 2012 Series
                     (redeemed)

December 15, 1983    Pollution Control Series C  Bonds of the Pollution Control
                     (redeemed)                  Series C

May 15, 1984         Pollution Control Series D  Bonds of the Pollution Control
                     (redeemed)                  Series D

March 1, 1985        Pollution Control Series E  Bonds of the Pollution Control
                     (redeemed)                  Series E

February 1, 1986     10 1/2% Series due 2016     Bonds of the First 2016 Series
                     (redeemed)

July 1, 1986         9 7/8% Series due 2016      Bonds of the Second 2016 Series
                     (redeemed)

September 1, 1986    9 3/8% Series due 2016      Bonds of the Third 2016 Series
                     (redeemed)

February 1, 1987     Pollution Control Series F  Bonds of the Pollution Control
                     (redeemed)                  Series F

February 1, 1987     Pollution Control Series G  Bonds of the Pollution Control
                     (redeemed)                  Series G

February 1, 1987     Pollution Control Series H  Bonds of the Pollution Control
                     (redeemed)                  Series H

July 1, 1987         Pollution Control Series I  Bonds of the Pollution Control
                     (redeemed)                  Series I

July 1, 1988         10% Series due 1998         Bonds of the Third 1998 Series
                     (redeemed)

July 1, 1991         Pollution Control Series J  Bonds of the Pollution Control
                                                 Series J

June 1, 1992         Pollution Control Series K  Bonds of the Pollution Control
                                                 Series K

June 1, 1992         Pollution Control Series L  Bonds of the Pollution Control
                                                 Series L

July 1, 1992         7.95% Series due 2004       Bonds of the Third 2004 Series

July 1, 1992         8 3/4% Series due 2021      Bonds of the 2021 Series
                     (redeemed)

                                       63


Date of Supplemental   Identification
    Indenture             of Series                      Called

September 1, 1992    6 1/2% Series due 1999      Bonds of the 1999 Series

February 15, 1993    8% Series due 2023          Bonds of the 2023 Series
                     (redeemed)

March 15, 1993       6 1/8% Series due 2000      Bonds of the 2000 Series

March 15, 1993       6 3/4% Series due 2005      Bonds of the 2005 Series

July 15, 1993        7 1/2% Series due 2025      Bonds of the 2025 Series

August 1, 1993       6 1/2% Series due 2003      Bonds of the Second 2003 Series

October 15, 1993     5 5/8% Series due 2000      Bonds of the Second 2000 Series

November 1, 1993     Pollution Control Series M  Bonds of the Pollution Control
                                                 Series M

November 1, 1993     Pollution Control Series N  Bonds of the Pollution Control
                                                 Series N

November 1, 1993     Pollution Control Series O  Bonds of the Pollution Control
                                                 Series O

April 1, 1997        Pollution Control Series P  Bonds of the Pollution Control
                                                 Series P

April 1, 1997        Pollution Control Series Q  Bonds of the Pollution Control
                                                 Series Q

April 1, 1997        Pollution Control Series R  Bonds of the Pollution Control
                                                 Series R

March 1, 1998        Pollution Control Series S  Bonds of the Pollution Control
                                                 Series S

March 1, 1998        Pollution Control Series T  Bonds of the Pollution Control
                                                 Series T

July 15, 1998        6 1/4% Series due 2002      Bonds of the 2002 Series

September 15, 1998   6% Series due 2003          Bonds of the Third 2003 Series


and

         WHEREAS,  the  Company  desires  to create a new  series of Bonds to be
  issued  under the Original  Indenture,  to be known as First  Mortgage  Bonds,
  7.50% Series due 2009 (the "Bonds of the 2009 Series") and to issue additional
                     Bonds under the Original Indenture; and

                                       64


     WHEREAS,  the Bonds of the 2009 Series are to be issued to Harris Trust and
Savings  Bank,  as trustee  (the "New  Mortgage  Trustee")  under the  Company's
General  Mortgage  Indenture and Deed of Trust dated as of November 1, 1992 (the
"New  Mortgage")  and are to be owned and held by the New  Mortgage  Trustee  as
"Pledged Bonds" (as defined in the New Mortgage) in accordance with the terms of
the New Mortgage; and

     WHEREAS, the Company, in the exercise of the powers and authority conferred
upon and  reserved to it under the  provisions  of the Original  Indenture,  and
pursuant to appropriate resolutions of the Board of Directors, has duly resolved
and  determined  to make,  execute  and  deliver to the  Trustee a  Supplemental
Indenture in the form hereof for the purposes herein provided; and

     WHEREAS,   all   conditions  and   requirements   necessary  to  make  this
Supplemental  Indenture a valid,  binding and legal  instrument  have been done,
performed and  fulfilled and the execution and delivery  hereof have been in all
respects duly authorized;

             NOW, THEREFORE, THIS SUPPLEMENTAL INDENTURE WITNESSETH:

     THAT Illinois Power Company, in consideration of the purchase and ownership
from  time  to  time  of the  Bonds  and the  service  by the  Trustee,  and its
successors,  under the Original  Indenture  and of One Dollar to it duly paid by
the  Trustee at or before the  ensealing  and  delivery of these  presents,  the
receipt whereof is hereby acknowledged,  hereby covenants and agrees to and with
the Trustee and its  successors in the trust under the Original  Indenture,  for
the benefit of the New Trustee and any successor holder of the Bonds as follows:


                                   ARTICLE I.

                    DESCRIPTION OF BONDS OF THE 2009 SERIES.

         SECTION 1. The Company hereby creates a new series of Bonds to be known
as "The First  Mortgage  Bonds,  7.50%  Series due 2009" (the "Bonds of the 2009
Series").  The Bonds of the 2009 Series  shall be  executed,  authenticated  and
delivered in  accordance  with the  provisions  of, and shall in all respects be
subject  to,  all  of the  terms,  conditions  and  covenants  of  the  Original
Indenture,  as supplemented  and modified.  The Bonds of the 2009 Series will be
issued only to the New Mortgage  Trustee as security for a series of bonds being
issued under the  Company's New Mortgage and the  supplemental  indenture to the
New  Mortgage  dated as of June 15,  1999 (the "New  Mortgage  Bonds of the 2009
Series").

         The Bonds of the 2009 Series shall be dated as provided in Section 6 of
Article II of the Original  Indenture and for the purposes of said Section 6 the
commencement  of the first interest  period shall be June 29, 1999. All Bonds of
the 2009 Series shall mature on June 15,  2009,  and shall bear  interest at the
rate of SEVEN AND ONE-HALF PER CENT (7.50%) per annum, payable  semi-annually on
June 15 and December 15 of each year,  commencing  December 15, 1999,  until the
principal  sum is paid in full.  Any payment by the Company of principal  of, or
interest  on, any Bonds of the 2009 Series  shall be applied by the New Mortgage
Trustee to the  payment of any  principal  or  interest,  as the case may be, in
respect of the New Mortgage Bonds of the 2009 Series due in accordance  with the
terms of the New Mortgage.

         SECTION 2. The Bonds of the 2009 Series and the  Trustee's  Certificate
shall be substantially in the following forms respectively:

                                       65


                             [FORM OF FACE OF BOND]

                             ILLINOIS POWER COMPANY
             (Incorporated under the laws of the State of Illinois)

                   FIRST MORTGAGE BOND, 7.50% SERIES DUE 2009

No.                                                                 $250,000,000

         ILLINOIS POWER COMPANY, a corporation  organized and existing under the
laws of the State of  Illinois  (the  "Company,"  which term shall  include  any
successor  corporation as defined in the Indenture hereinafter referred to), for
value  received,  hereby  promises to pay to Harris  Trust and  Savings  Bank as
trustee  (the "New  Mortgage  Trustee")  under the  Company's  General  Mortgage
Indenture and Deed of Trust dated as of November 1, 1992 (the "New Mortgage") or
its  registered  assigns,  the  principal  sum of Two Hundred and Fifty  Million
Dollars  ($250,000,000)  on June 15, 2009, in any coin or currency of the United
States of America  which at the time of  payment is legal  tender for public and
private  debts,  and to pay interest  thereon in like coin or currency from June
29,  1999,  payable  semi-annually  on June  15 and  December  15 in each  year,
commencing December 15, 1999, at the rate of SEVEN AND ONE-HALF PER CENT (7.50%)
per annum,  until the Company's  obligation  with respect to the payment of such
principal  shall be discharged as provided in the Indenture.  Both the principal
of, and the  interest  on, this Bond are payable at the agency of the Company in
the City of Chicago, Illinois.

         This First Mortgage Bond shall not be entitled to any benefit under the
Indenture or any indenture  supplemental  thereto, or become valid or obligatory
for any purpose,  until the form of certificate  endorsed hereon shall have been
signed by or on behalf of Harris Trust and Savings  Bank,  the Trustee under the
Indenture, or a successor trustee thereto under the Indenture (the "Trustee").

         The provisions of this First Mortgage Bond are continued on the reverse
hereof and such continued provisions shall for all purposes have the same effect
as though fully set forth at this place.

         IN WITNESS  WHEREOF,  Illinois  Power  Company  has  caused  this First
Mortgage Bond to be signed  (manually or by facsimile  signature) in its name by
its  President  or a Vice  President,  and its  corporate  seal (or a  facsimile
thereof) to be hereto affixed and attested (manually or by facsimile  signature)
by its Secretary or an Assistant Secretary.


Dated:                                            ILLINOIS POWER COMPANY,



                                                  By:
                                                     ---------------------------
                                                          Vice President

(Corporate Seal)

ATTEST:


- -------------------------------------
Secretary or Assistant Secretary

                                       66


                         [FORM OF TRUSTEE'S CERTIFICATE]

         This First  Mortgage Bond is one of the Bonds of the series  designated
therein,  described  in the  within-mentioned  Indenture  and  the  Supplemental
Indenture dated as of June 15, 1999.


                                                  HARRIS TRUST AND SAVINGS BANK,
                                                    Trustee

                                                  By:
                                                     ---------------------------
                                                         Authorized Officer

                            [FORM OF REVERSE OF BOND)

         This First Mortgage Bond is one of a duly authorized  issue of Bonds of
the Company (the "Bonds") in unlimited aggregate principal amount, of the series
hereinafter specified,  all issued and to be issued under and equally secured by
the  Mortgage  and Deed of Trust  (the  "Indenture"),  dated  November  1, 1943,
executed by the Company to Harris  Trust and Savings  Bank (the  "Trustee"),  as
Trustee, to which Indenture and all indentures  supplemental thereto,  including
the  Supplemental  Indenture dated February 15, 1993, which amended Section 1 of
Article IX of the  Indenture,  reference is hereby made for a description of the
properties  mortgaged and pledged,  the nature and extent of the  security,  the
rights of the  registered  owners of the Bonds  and of the  Trustee  in  respect
thereof,  and the terms and conditions  upon which the Bonds are, and are to be,
secured.  The Bonds may be issued in series,  for various  principal  sums,  may
mature  at  different  times,  may bear  interest  at  different  rates  and may
otherwise vary as in the Indenture provided.  This First Mortgage Bond is one of
a series  designated  as the First  Mortgage  Bonds,  7.50% Series Due 2009 (the
"Bonds of the 2009  Series") of the Company,  unlimited  in aggregate  principal
amount,  issued  under  and  secured  by  the  Indenture  and  described  in the
supplemental indenture dated as of June 15, 1999 (the "Supplemental Indenture of
June 15,  1999"),  between  the  Company and the  Trustee,  supplemental  to the
Indenture.

         The Bonds of the 2009 Series are subject to redemption on the terms and
subject to the  conditions set forth in the  Supplemental  Indenture of June 15,
1999.

     To  the  extent   permitted   by,  and  as  provided  in,  the   Indenture,
modifications or alterations of the Indenture,  or of any indenture supplemental
thereto,  and of the rights and obligations of the Company and of the holders of
the  Bonds  and  coupons  may be made  with the  consent  of the  Company  by an
affirmative  vote of the holders of not less than 66 2/3% in amount of the Bonds
entitled to vote then outstanding,  at a meeting of Bondholders  called and held
as provided in the Indenture,  and by an affirmative  vote of the holders of not
less than 66 2/3% in amount of the  Bonds of any  series  entitled  to vote then
outstanding and affected by such modification or alteration, in case one or more
but less than all of the series of Bonds then  outstanding  under the  Indenture
are so affected; provided however, that no such modification or alteration shall
be made which will

                                       67


affect the terms of payment of the principal of, or interest or premium, if any,
on this First Mortgage Bond.

         In case an Event of Default, as defined in the Indenture,  shall occur,
the principal of all the Bonds at any such time outstanding  under the Indenture
may be declared or may become due and payable,  upon the  conditions  and in the
manner and with the effect  provided in the  Indenture.  The Indenture  provides
that such  declaration  may in certain  events be  rescinded by the holders of a
majority in principal amount of the Bonds outstanding.

         No  recourse  shall be had for the  payment  of the  principal  of,  or
premium or interest on this First  Mortgage  Bond, or for any claim based hereon
or  on  the  Indenture  or  any  indenture  supplemental  thereto,  against  any
incorporator,  or against any stockholder,  director or officer,  as such, past,
present  or  future,  of  the  Company,  or  of  any  predecessor  or  successor
corporation,  either directly or through the Company or any such  predecessor or
successor corporation, whether by virtue of any constitution, statute or rule of
law, or by the  enforcement of any assessment or penalty or otherwise,  all such
liability, whether at common law, in equity, by any constitution,  statute, rule
of law, or  otherwise,  of  incorporators,  stockholders,  directors or officers
being  released by every owner hereof by the  acceptance of this First  Mortgage
Bond and as part of the consideration  for the issue hereof,  and being likewise
released by the terms of the Indenture;  provided,  however, that nothing herein
or in the  Indenture  or any  indenture  supplemental  thereto  contained  shall
prevent  the  enforcement  of the  liability,  if  any,  of any  stockholder  or
subscriber  to capital  stock upon or in respect of shares of capital  stock not
fully paid up.

         Notwithstanding  any  provision  in  the  Indenture,  the  Supplemental
Indenture  of June 15, 1999 or this First  Mortgage  Bond to the  contrary,  any
payment by the Company  under the New Mortgage of principal  of, or interest on,
bonds which shall have been  authenticated  and delivered under the New Mortgage
(the "New Mortgage Bonds of the 2009 Series") upon the basis of the issuance and
delivery to the New Mortgage  Trustee of the Bonds of the 2009 Series shall,  to
the extent  thereof,  be deemed to satisfy and discharge  the  obligation of the
Company  to make a payment  of  principal  or  interest,  as the case may be, in
respect of this First Mortgage Bond which is then due.

         This First  Mortgage Bond  constitutes a "Pledged  Bond" (as defined in
the  New  Mortgage)  and  is  subject  to all of  the  rights  and  restrictions
applicable to Pledged Bonds as set forth in the New Mortgage.  Without  limiting
the  generality of the  foregoing,  this First Mortgage Bond shall be subject to
surrender by the New  Mortgage  Trustee in  accordance  with the  provisions  of
Section  7.03 of the New  Mortgage.  To the extent  that any  provisions  in the
Indenture,  the  Supplemental  Indenture of June 15, 1999 or this First Mortgage
Bond are inconsistent with the provisions relating to Pledged Bonds that are set
forth in the New Mortgage, the provisions of the New Mortgage shall apply.

         SECTION 3.  Notwithstanding  any  provision in the Original  Indenture,
this  Supplemental  Indenture,  or the Bonds of the 2009 Series to the contrary,
any payment by the Company  under the New Mortgage of principal  of, or interest
on, New  Mortgage  Bonds of the 2009 Series upon the basis of the  issuance  and
delivery to the New Mortgage  Trustee of the Bonds of the 2009 Series shall,  to
the extent thereof, be deemed to satisfy and discharge the obligation of the

                                       68


Company to make any payment of  principal  or  interest,  as the case may be, in
respect of the Bonds of the 2009 Series which is then due.

         SECTION 4. The Bonds of the 2009 Series constitute  "Pledged Bonds" (as
defined  in the  New  Mortgage)  and  are  subject  to all  of  the  rights  and
restrictions  applicable  to  Pledged  Bonds as set  forth in the New  Mortgage.
Without  limiting the generality of the foregoing,  the Bonds of the 2009 Series
shall be subject to surrender by the New Mortgage Trustee in accordance with the
provisions  of  Section  7.03  of the  New  Mortgage.  To the  extent  that  any
provisions in the Original Indenture,  this Supplemental  Indenture or the Bonds
of the 2009  Series are  inconsistent  with the  provisions  relating to Pledged
Bonds that are set forth in the New Mortgage, the provisions of the New Mortgage
shall apply.


                                   ARTICLE II.

                       ISSUE OF BONDS OF THE 2009 SERIES.

         SECTION  1. The  Company  hereby  exercises  the  right to  obtain  the
authentication of $250,000,000  principal amount of additional Bonds pursuant to
the terms of Section 6 of Article III of the Original  Indenture in substitution
for  refundable  Bonds.  All such  additional  Bonds  shall be Bonds of the 2009
Series.

         SECTION  2. Such  Bonds of the 2009  Series  may be  authenticated  and
delivered prior to the filing for recordation of this Supplemental Indenture.

         SECTION 3.  Notwithstanding  any provision in the Original Indenture to
the  contrary,  execution  of the  Bonds of the 2009  Series  on  behalf  of the
Company,  and the attesting of the corporate seal of the Company  affixed to the
Bonds of the 2009 Series by the  officers of the Company  authorized  to do such
acts by Section 12 of Article II of the Original  Indenture  may be validly done
either by the manual or the facsimile  signatures of such authorized officers of
the Company.


                                  ARTICLE III.

                                   REDEMPTION.

         The  Company at its option  may,  at any time,  redeem the Bonds of the
2009 Series,  in whole or in part (if in part, by lot or by such other method as
the Trustee shall deem fair or appropriate) prior to maturity, on any date, upon
payment of a redemption  price equal to the greater of (i) 100% of the principal
amount of the Bonds of the 2009  Series to be redeemed  plus  accrued and unpaid
interest thereon, if any, from the last interest payment date to the date of

                                       69


redemption,  or (ii) the Make Whole Amount plus accrued and unpaid interest,  if
any, from the last interest payment date to the redemption date.

     "Make Whole Amount" means, with respect to a Bond of the 2009 Series at any
time,  the sum of the present  values of the  Remaining  Scheduled  Payments (as
defined  below)  discounted,  on a  semiannual  basis  assuming  a 360-day  year
consisting  of twelve 30-day  months),  at a rate equal to the Treasury Rate (as
defined below) plus 20 basis points.  The Make Whole Amount shall be computed as
of  the  third  Business  Day  prior  to the  applicable  redemption  date,  and
certified, by an Investment Banker (as defined below).

     "Investment Banker" means an independent  investment banking institution of
good standing selected by the Company.

     "Remaining Scheduled Payments" means the remaining scheduled payment of the
principal  and interest  that would be due if such Bonds of the 2009 Series were
not  redeemed.  However,  if the  redemption  date is not a  scheduled  interest
payment date, the amount of the next succeeding  scheduled  interest  payment on
such Bond of the 2009 Series  will be reduced by the amount of interest  accrued
on such New Mortgage Bonds of the 2009 Series to such redemption date.

     "Treasury  Rate"  means an annual rate equal to the  semiannual  equivalent
yield to maturity of the Comparable Treasury Issue (as defined below),  assuming
a price for the  Comparable  Treasury  Issue  (expressed  as a percentage of its
principal amount) equal to the Comparable  Treasury Price (as defined below) for
the  redemption  date.  The  semiannual  equivalent  yield to  maturity  will be
computed as of the third Business Day immediately preceding the redemption date.

     "Comparable  Treasury  Issue"  means the United  States  Treasury  security
selected by Salomon Smith Barney Inc. or J.P.  Morgan  Securities  Inc. or their
affiliates as having a maturity comparable to the remaining term of the Bonds of
the  2009  Series  that  would be  utilized,  at the  time of  selection  and in
accordance with customary financial practice, in pricing new issues of corporate
debt securities of comparable maturity to the remaining term of the Bonds of the
2009 Series.

     "Comparable  Treasury Price" means the average of three Reference  Treasury
Dealer  Quotations (as defined below) obtained by the Trustee for the redemption
date.

     "Reference  Treasury  Dealers"  means  Salomon  Smith  Barney Inc. and J.P.
Morgan  Securities Inc. (so long as they continue to be primary U.S.  Government
securities dealers) and any one other primary U.S. Government  securities dealer
chosen by the  Company.  If either  Salomon  Smith  Barney Inc.  or J.P.  Morgan
Securities Inc. ceases to be a primary U.S.  Government  securities  dealer, the
Company  will  appoint in its place  another  nationally  recognized  investment
banking firm that is a primary U.S. Government securities dealer.

     "Reference  Treasury Dealer Quotation" means the average,  as determined by
the  Trustee,  of the bid and asked  prices for the  Comparable  Treasury  Issue
(expressed in each case as a

                                       70


percentage  of its  principal  amount)  quoted in  writing  to the  Trustee by a
Reference  Treasury  Dealer  at 3:30  p.m.,  New York  City  time,  on the third
Business Day preceding the redemption date.


                                   ARTICLE IV.

                                  THE TRUSTEE.

         The Trustee hereby accepts the trusts hereby declared and provided, and
agrees  to  perform  the same  upon the terms  and  conditions  in the  Original
Indenture set forth and upon the following terms and conditions:

                  The Trustee shall not be responsible in any manner  whatsoever
         for or in respect of the validity or sufficiency  of this  Supplemental
         Indenture  or the due  execution  hereof  by the  Company  or for or in
         respect of the recitals  contained  herein,  all of which  recitals are
         made by the  Company  solely.  In  general,  each  and  every  term and
         condition  contained in Article XIII of the  Original  Indenture  shall
         apply to this Supplemental  Indenture with the same force and effect as
         if the  same  were  herein  set  forth in full,  with  such  omissions,
         variations and modifications  thereof as may be appropriate to make the
         same conform to this Supplemental Indenture.


                                   ARTICLE V.

                            MISCELLANEOUS PROVISIONS.

         This  Supplemental  Indenture  may be  simultaneously  executed  in any
number of counterparts,  each of which when so executed shall be deemed to be an
original;  but such counterparts shall together  constitute but one and the same
instrument.

                                       71


         IN WITNESS WHEREOF, Illinois Power Company has caused this Supplemental
Indenture to be executed on its behalf by its Chairman and President, one of its
Executive Vice Presidents,  one of its Senior Vice Presidents or one of its Vice
Presidents  and its corporate  seal to be hereto  affixed and said seal and this
Supplemental  Indenture to be attested by its  Secretary or one of its Assistant
Secretaries;  and said  Harris  Trust  and  Savings  Bank,  in  evidence  of its
acceptance of the trust hereby created,  has caused this Supplemental  Indenture
to be executed on its behalf by its President or one of its Vice  Presidents and
its  corporate  seal to be hereto  affixed  and said seal and this  Supplemental
Indenture to be attested by its Secretary or one of its  Assistant  Secretaries,
all as of the date first written above.

                                          ILLINOIS POWER COMPANY


                                          By
                                            ------------------------------------
                                               Robert A. Schultz
                                               Vice President - Finance


(CORPORATE SEAL)


ATTEST:


- ---------------------------
Leah Manning Stetzner
Corporate Secretary

                                          HARRIS TRUST AND SAVINGS BANK, Trustee


                                          By
                                            ------------------------------------
                                               J. Bartolini
                                               Vice President

(CORPORATE SEAL)

ATTEST:


- ------------------------------
C. Potter
Assistant Secretary

                                       72


STATE OF ILLINOIS    )
                     )SS.:
COUNTY OF MACON      )

         BE IT REMEMBERED,  that on this ____ day of _____, 1999, before me, the
undersigned,  a Notary  Public  within and for the  County and State  aforesaid,
personally  came Robert A.  Schultz,  Vice  President - Finance and Leah Manning
Stetzner,  Corporate  Secretary,  of Illinois Power Company,  a corporation duly
organized,  incorporated  and existing  under the laws of the State of Illinois,
who are personally known to me to be such officers, and who are personally known
to me to be the same persons who executed as such officers the within instrument
of writing,  and such persons  duly  acknowledged  that they signed,  sealed and
delivered  the said  instrument as their free and voluntary act as such officers
and as the free and voluntary  act of said  Illinois  Power Company for the uses
and purposes therein set forth.

         IN WITNESS WHEREOF,  I have hereunto  subscribed my name and affixed my
official seal on the day and year last above written.



                                          --------------------------------------
                                          Notary Public, Macon County, Illinois

My Commission Expires on _________________.

(NOTARIAL SEAL)


STATE OF ILLINOIS    )
                     )SS.:
COUNTY OF COOK       )

         BE IT REMEMBERED,  that on this ___ day of ______, 1999, before me, the
undersigned,  a Notary  Public  within and for the  County and State  aforesaid,
personally  came  J.  Bartolini,   Vice  President,  and  C.  Potter,  Assistant
Secretary,  of Harris Trust and Savings  Bank,  a  corporation  duly  organized,
incorporated  and  existing  under  the laws of the State of  Illinois,  who are
personally  known to me to be such officers,  and who are personally known to me
to be the same persons who executed as such  officers the within  instrument  of
writing,  and such  persons  duly  acknowledged  that they  signed,  sealed  and
delivered  the said  instrument as their free and voluntary act as such officers
and as the free and  voluntary act of said Harris Trust and Savings Bank for the
uses and purposes therein set forth.

         IN WITNESS WHEREOF,  I have hereunto  subscribed my name and affixed my
official seal on the day and year last above written.


                                          --------------------------------------
                                          Notary Public, Cook County, Illinois

My Commission Expires on ______________.
(NOTARIAL SEAL)

                                       73


         Return To:                       This Instrument Was Prepared By:

         ILLINOIS POWER COMPANY           SCHIFF HARDIN & WAITE
         Real Estate Dept. F-14           6600 Sears Tower
         500 S. 27th Street               233 South Wacker Drive
         Decatur, IL 62525                Chicago, IL  60606

                                       74