Company: AILIM
Filing Date: 2025-09-16
Form Type: 424B2
Source: 0001104659-25-090464
Chunk: 35

Company: Ameren Illinois Co
Filing Date: 2025-09-16
Form: 424B2
Chunk 35
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 New York, New York. Pillsbury Winthrop Shaw Pittman LLP represents certain of our affiliates from time to time in connection with various matters. All matters pertaining to our incorporation and all other matters of Illinois law relating to us will be passed upon only by Mr. Lee. As to all matters based on the law of the State of Illinois, Morgan, Lewis & Bockius LLP will rely on the opinion of Mr. Lee. As to all matters based on the law of the State of New York, Mr. Lee will rely on the opinion of Morgan, Lewis & Bockius LLP.

### EXPERTS
The financial statements incorporated in this prospectus by reference to the Annual Report on Form 10-K for the year ended December 31, 2024 have been so incorporated in reliance on the report of PricewaterhouseCoopers LLP, an independent registered public accounting firm, given on the authority of said firm as experts in auditing and accounting.

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TABLE OF CONTENTS

### PROSPECTUS

### AMEREN ILLINOIS COMPANY

#### Senior Secured Debt Securities

#### First Mortgage Bonds

#### Senior Unsecured Debt Securities

#### Preferred Stock
Ameren Illinois Company may offer any of the securities described in this prospectus in one or more offerings from time to time in amounts authorized from time to time. This prospectus may also be used by selling securityholders of the securities described herein.

This prospectus provides you with a general description of these securities. We will provide specific information about the offering and the terms of these securities in supplements to this prospectus. The supplements may also add, update or change information contained in this prospectus. You should read this prospectus and the supplements carefully before investing. This prospectus may not be used to sell any of these securities unless accompanied by a prospectus supplement.

Unless otherwise indicated in the applicable prospectus supplement, we do not intend to list the securities described in this prospectus on a national securities exchange.

Our principal executive offices are located at 10 Richard Mark Way, Collinsville, Illinois 62234 and our telephone number is (618) 343-8150.

Investing in our securities involves risks. Before buying our securities, you should refer to the risk factors included in our annual, quarterly and current reports filed with the Securities and Exchange Commission under the Securities Exchange Act of 1934, as amended, which are incorporated by reference into this prospectus, in prospectus supplements relating to specific