Company: AILIM
Filing Date: 2025-09-16
Form Type: 424B2
Source: 0001104659-25-090464
Chunk: 3

Company: Ameren Illinois Co
Filing Date: 2025-09-16
Form: 424B2
Chunk 3
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 prospectus are part of a registration statement that we have filed with the Securities and Exchange Commission, or SEC, utilizing a “shelf” registration process. Under this shelf registration process, we may sell, at any time and from time to time, in one or more offerings, any of the securities described in the accompanying prospectus, including the bonds, in an unspecified amount, of which this offering is a part. In this prospectus supplement, we provide you with specific information about the terms of the bonds and this offering.

### AMEREN ILLINOIS COMPANY
Ameren Illinois Company, doing business as Ameren Illinois, operates rate-regulated electric transmission, electric distribution, and natural gas distribution businesses in Illinois. Ameren Illinois is a subsidiary of Ameren Corporation (“Ameren”), a public utility holding company. Ameren Illinois was incorporated in Illinois in 1923 and is the successor to a number of companies, the oldest of which was organized in 1902. Ameren Illinois supplies electric and natural gas utility service to a 43,700 square mile area in central and southern Illinois. Ameren Illinois supplies electric service to 1.2 million customers and natural gas service to 0.8 million customers. Our principal executive offices are located at 10 Richard Mark Way, Collinsville, Illinois 62234, and our telephone number is (618) 343-8150.

### RISK FACTORS
Investing in the bonds involves certain risks. In considering whether to purchase the bonds offered by this prospectus supplement, you should carefully consider the information included or incorporated by reference in this prospectus supplement and the accompanying prospectus. In particular, you should carefully consider the information under the heading “Risk Factors” in our Annual Report on Form 10-K for the year ended December 31, 2024(our “2024 Form 10-K”), which is incorporated by reference in this prospectus supplement and the accompanying prospectus.

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### WHERE YOU CAN FIND MORE INFORMATION
We have filed a registration statement on Form S-3 with the SEC under the Securities Act of 1933, as amended (the “Securities Act”). This prospectus supplement and the accompanying prospectus are part of the registration statement, but the registration statement also contains or incorporates by reference additional information and exhibits. We are subject to the informational requirements of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), and, therefore