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): April 22, 2013

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

At the annual meeting of shareholders of each of Ameren, Union Electric Company d/b/a Ameren Missouri (“Ameren Missouri”) and Ameren Illinois Company d/b/a Ameren Illinois (“Ameren Illinois”) held on April 23, 2013 (each, its respective “Annual Meeting”), the matters listed below were submitted to a vote of its respective shareholders.

Item (1): Election of Directors

Ameren

Ameren shareholders elected the following ten nominees, each of whom was named in Ameren’s definitive proxy statement relating to the Annual Meeting, to serve as directors until Ameren’s next annual meeting of shareholders in 2014 and until their respective successors have been duly elected and qualified. Information as to the vote on each director standing for election is provided below:

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Ameren Missouri

At Ameren Missouri’s annual meeting of shareholders held on April 23, 2013, the following individuals (comprising Ameren Missouri’s full Board of Directors) were elected to serve until the next annual meeting of shareholders in 2014 and until their respective successors have been duly elected and qualified: Warner L. Baxter, Daniel F. Cole, Adam C. Heflin, Martin J. Lyons, Jr., Michael L. Moehn, Charles D. Naslund and Gregory L. Nelson. Each individual received 102,123,834 votes for election and no withheld votes, abstentions or broker non-votes.

Ameren Illinois

At Ameren Illinois’ annual meeting of shareholders held on April 23, 2013, the following individuals (comprising Ameren Illinois’ full Board of Directors) were elected to serve until the next annual meeting of shareholders in 2014 and until their respective successors have been duly elected and qualified: Daniel F. Cole, Martin J. Lyons, Jr., Richard J. Mark and Gregory L. Nelson. Each individual received 25,452,373 votes for election and no withheld votes, abstentions or broker non-votes.

Item (2): Advisory Approval of Executive Compensation

Ameren shareholders approved, on an advisory basis, the compensation of certain executives as disclosed in the Compensation Discussion and Analysis, the compensation tables and other narrative executive compensation disclosures in the definitive proxy statement relating to the Annual Meeting, as set forth below:

Item (3): Ratification of the Appointment of Independent Registered Public Accounting Firm for the Fiscal Year Ending December 31, 2013

Ameren shareholders ratified the appointment of PricewaterhouseCoopers LLP as Ameren’s independent registered public accounting firm for the fiscal year ending December 31, 2013, as set forth below:

Item (4): Shareholder Proposal Relating to Report on Reducing Risk in Energy Portfolio Through Increased Energy Efficiency and Renewable Energy Resources

Ameren shareholders did not approve a shareholder proposal requesting a report, to be reviewed by a Board committee comprised of independent Ameren directors, on actions the

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Company is taking or could take to reduce risk throughout its energy portfolio by diversifying the Company’s energy resources to include increased energy efficiency and renewable energy resources, as described in the definitive proxy statement relating to the Annual Meeting, as set forth below:

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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: April 23, 2013

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