UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of the
Securities Exchange Act of 1934

Date of report (Date of earliest event reported): May 14, 2026

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrants under any of the following provisions:

¨ Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

¨ Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

¨ Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

¨ Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Securities registered pursuant to Section 12(b) of the Act:

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§240.12b-2 of this chapter).

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act.

ITEM 5.07 Submission of Matters to a Vote of Security Holders.

At the annual meeting of shareholders of each of Ameren Corporation (“Ameren”), Union Electric Company, doing business as Ameren Missouri (“Ameren Missouri”), and Ameren Illinois Company, doing business as Ameren Illinois (“Ameren Illinois”), held on May 14, 2026 (“Annual Meeting”), the matters listed below were submitted to a vote of each company’s respective shareholders.

Ameren

Item (1): Election of Directors

The following individuals (comprising Ameren’s full Board of Directors) were elected:

Item (2): Advisory Approval of Executive Compensation

Item (3): Ratification of the Appointment of PricewaterhouseCoopers LLP as Independent Registered Public Accounting Firm for the Fiscal Year Ending December 31, 2026

Ameren Missouri

Item (1): Election of Directors

At Ameren Missouri’s Annual Meeting, the following individuals (comprising Ameren Missouri’s full Board of Directors) were elected: Michael L. Moehn, Ajay K. Arora, David M. Feinberg, Ryan J. Martin, and Leonard P. Singh. Each individual received 102,123,834 votes for election and no withheld votes, abstentions or broker non-votes.

Ameren Illinois

Item (1): Election of Directors

At Ameren Illinois’ Annual Meeting, the following individuals (comprising Ameren Illinois’ full Board of Directors) were elected: Patrick E. Smith Sr., David M. Feinberg, Michael L. Moehn, Theresa A. Shaw, and Leonard P. Singh. Each individual received 25,452,373 votes for election and no withheld votes, abstentions or broker non-votes.

This combined Form 8-K is being filed separately by Ameren Corporation, Union Electric Company and Ameren Illinois Company (each a “registrant”). Information contained herein relating to any individual registrant has been filed by such registrant on its own behalf. No registrant makes any representation as to information relating to any other registrant.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, each registrant has duly caused this report to be signed on its behalf by the undersigned thereunto duly authorized. The signature for each undersigned company shall be deemed to relate only to matters having reference to such company or its subsidiaries.

Date: May 18, 2026