Company: AILIM
Filing Date: 2025-09-16
Form Type: 424B2
Source: 0001104659-25-090464
Chunk: 6

Company: Ameren Illinois Co
Filing Date: 2025-09-16
Form: 424B2
Chunk 6
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 secured debt (including current maturities) | ​ | ​ | ​                   | ​ |  6,208 | ​ | ​ | ​ | ​                              | ​ |   44.8 | ​ | ​ |
| Preferred stock                                                                 | ​ | ​ | ​                   | ​ |     49 | ​ | ​ | ​ | ​                              | ​ |    0.3 | ​ | ​ |
| Other shareholders’ equity                                                      | ​ | ​ | ​                   | ​ |  7,620 | ​ | ​ | ​ | ​                              | ​ |   54.9 | ​ | ​ |
| Total capitalization                                                            | ​ | ​ | ​                   | $ | 13,877 | ​ | ​ | ​ | ​                              | ​ | 100.0% | ​ | ​ |

(1) Consists of commercial paper. (2) Includes the principal amount of the related long-term debt and therefore excludes unamortized net debt discount and premium of $10 million and unamortized debt issuance costs of $53 million. (3) Includes approximately $1,183 million in principal amount of senior secured debt securities secured by first mortgage bonds and approximately $4,780 million in principal amount of first mortgage bonds. USE OF PROCEEDS We estimate that the net proceeds from the sale of the bonds offered by this prospectus supplement (after deducting the underwriting discount and our other expenses of the offering) will be approximately $356.5 million. We intend to use the net proceeds of this offering to repay a portion of our short-term debt. On September 12, 2025, our short-term debt consisted of our commercial paper, which was outstanding in the amount of approximately $207.0 million and had maturities of up to 3 days and a weighted-average interest rate of 4.49%.

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TABLE OF CONTENTS

### DESCRIPTION OF BONDS
The following description of the bonds is only a summary and is not intended to be comprehensive. The description should be read together with the description set forth in the accompanying prospectus under the heading “Description of First Mortgage Bonds and Mortgage Indenture.” In the event that information in this prospectus supplement is inconsistent with information in the accompanying prospectus, you should rely on the information in this prospectus supplement.

#### General
We are issuing $350,000,000 in principal amount of bonds as a further issuance of an existing series of first mortgage bonds under, and secured by