Union Electric Co., also known as Ameren Missouri, is a rate-regulated electric and natural gas utility headquartered in St. Louis, Missouri. The company was incorporated in Missouri in 1922, with its origins tracing back to 1881 or 1902, and is a wholly owned subsidiary of Ameren Corporation (NYSE: AEE). As of March 2026, Union Electric Co. reported a trailing 12-month revenue of $4.77 billion and has approximately 3,830 full-time employees, with a market capitalization of about $7.5 billion as of May 2026.
Union Electric Co. is engaged in the generation, transmission, and distribution of electricity, as well as the distribution of natural gas. It provides electric service to approximately 1.2 million customers and natural gas service to about 0.1 million customers across a 24,000 square-mile area in central and eastern Missouri, including the greater St. Louis metropolitan area. The company generates electricity using a diverse mix of energy sources, including coal, nuclear, natural gas, hydroelectric, methane gas, and solar.
In terms of patent litigation, Union Electric Co. appears to be an operating company with a posture as a two-way litigant. The company has been involved in two tracked cases: one as a plaintiff and one as a defendant. This indicates that while it may defend against assertions, it also actively asserts its own intellectual property.
Notable cases include its role as a defendant in Midwest Energy Emissions Corp. et al. v. Berkshire Hathaway Energy Company et al. in the Southern District of Iowa, and as a plaintiff in Union Electric Co. v. Birchtech Corp. at the Patent Trial and Appeal Board. The defendant case's venue in the Southern District of Iowa aligns with Ameren Missouri's service territory, which includes parts of Iowa.