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                                                                    Exhibit 99.1

                                                             One Ameren Plaza
                                                             1901 Chouteau
                                                             Avenue
                                                             St. Louis, MO 63103

Contact:

Media                           Analysts                  Investors
Susan Gallagher                 Bruce Steinke             Investor Services
(314) 554-2175                  (314) 554-2574            invest@ameren.com
sgallagher@ameren.com           bsteinke@ameren.com


FOR IMMEDIATE RELEASE
- ---------------------


             Illinois Power Company Announces Partial Redemption and
            Cash Tender Offer for its 11.50% Mortgage Bonds due 2010


St. Louis,  Mo.,  Oct. 15,  2004---Illinois  Power  Company,  doing  business as
AmerenIP and a subsidiary of Ameren Corporation  (NYSE: AEE),  announced today a
redemption of  $192,500,000  aggregate  principal  amount of its mortgage bonds,
11.50%  Series  due  2010  ("Bonds")  and a cash  tender  offer  for any and all
remaining Bonds ($357,500,000 aggregate principal amount). The CUSIP numbers for
the Bonds are 452092 CK 3 and  452092 CM 9.  The redemption and tender offer are
part of  Ameren's  plan to improve  AmerenIP's  financial  profile and lower its
financing costs,  following the Sept. 30, 2004, acquisition of Illinois Power by
Ameren.

Partial Redemption
- ------------------

     Pursuant to an equity  clawback  provision,  AmerenIP  has  unconditionally
called for redemption on Nov. 15, 2004,  $192,500,000 aggregate principal amount
of its Bonds at a price  equal to $1,115 per $1,000  principal  amount of Bonds,
together with accrued and unpaid interest to the redemption date.

     The Bonds will be redeemed  with equity  contributed  to AmerenIP by Ameren
and will be selected in accordance  with the  applicable  procedures for partial
redemptions of The Depository Trust Company, the registered holder of the Bonds.

     Copies of the notice of  redemption  may be obtained from Ameren by calling
Investor Services at (314) 554-3502 (St. Louis) or (800) 255-2237 (toll free).

                                    - more -
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Cash Tender Offer
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     AmerenIP is offering to purchase for cash any and all of its Bonds that are
not redeemed  pursuant to the equity clawback  provision.  Following the partial
redemption of the Bonds,  $357,500,000  aggregate principal amount of Bonds will
remain  outstanding  and are eligible to  participate  in the tender offer.  The
purchase  price will be  determined,  as described in the Offer to Purchase,  in
accordance  with  standard  market  practice by reference to a yield of 50 basis
points over the yield on the 2.625% U.S. Treasury Note due Nov. 15, 2006, on the
price  determination  date. The price  determination  date is scheduled for 2:00
p.m.,  New York City time,  on Nov. 18,  2004.  The tender offer is scheduled to
expire at 5:00 p.m., New York City time, on Nov. 22, 2004. AmerenIP reserves the
right to extend or terminate the tender offer.

     The tender offer is not  conditioned  on any minimum  number of Bonds being
tendered. The tender offer is, however, subject to other conditions discussed in
the  Offer  to  Purchase.  The  tender  offer is also  intended  to  satisfy  an
obligation to offer to purchase  outstanding Bonds resulting from the "change of
control" of Illinois Power.

     This release is merely a  notification  that the tender offer exists and is
not an offer for the tender of the Bonds, which is only being made by the tender
offer materials. If you are interested in participating in the tender offer, you
should review all of the  information  regarding the terms and conditions of the
tender offer in the Offer to Purchase and related documentation.  For additional
information or for copies of the Offer to Purchase or the other offer documents,
you may call Global Bondholder Services  Corporation,  the information agent, at
(212)  430-3774  (collect)  or  toll-free  at (866)  470-4500.  The sole  dealer
managers for the tender offer are J.P.  Morgan  Securities  Inc.  (866) 834-4666
(toll free) and Lehman Brothers Inc. (212) 528-7581 (collect) and (800) 438-3242
(toll free).

     AmerenIP,  a regulated utility based in Decatur,  Ill., and a subsidiary of
Ameren,  serves  more than  590,000  electricity  customers  and nearly  415,000
natural gas customers over 15,000 square miles in northern, central and southern
Illinois. With assets of $17 billion,  Ameren, through its subsidiaries,  serves
2.3 million  electric  customers and 900,000 natural gas customers over a 64,000
square-mile area of Missouri and Illinois.

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