Company: AILIM
Filing Date: 2025-09-16
Form Type: 424B2
Source: 0001104659-25-090464
Chunk: 37

Company: Ameren Illinois Co
Filing Date: 2025-09-16
Form: 424B2
Chunk 37
---
 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 this prospectus and selling securityholders may offer such securities owned by them from time to time. We may offer any of the following securities: senior secured debt securities, first mortgage bonds, senior unsecured debt securities and preferred stock (collectively, the “securities”).

This prospectus provides you with a general description of the securities that may be offered by us and/or selling securityholders. Each time we offer securities, we will provide a prospectus supplement that will contain specific information about the terms of that offering. Any prospectus supplement may also add, update or change information contained in this prospectus. If there is any inconsistency between the information in this prospectus and the prospectus supplement, you should rely on the information in the prospectus supplement. The registration statement we have filed with the SEC includes exhibits that provide more detail regarding the securities described in this prospectus. You should read this prospectus, the registration statement of which this prospectus is a part and the related exhibits filed with the SEC and any prospectus supplement together with additional information described under “Where You Can Find More Information.”

In this prospectus, “Ameren Illinois,” “we,” “us” and “our” refer to Ameren Illinois Company and, unless the context otherwise indicates, do not include any of its subsidiaries, if any.

### 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 successor to a number of companies, the oldest of which was organized in 1902. Ameren Illinois supplies electric and natural gas 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.

TABLE OF CONTENTS

### RISK FACTORS
Investing in the securities involves certain risks. You are urged to read and consider the risk factors relating to an investment in the securities described in our annual, quarterly and current reports filed with the SEC under the Securities Exchange Act of 193