Ameren Corporation (NYSE: AEE) is a public utility holding company headquartered in St. Louis, Missouri, U.S.. Founded on December 31, 1997, through the merger of Union Electric Company and Central Illinois Public Service Company, Ameren operates as a Fortune 500 company. As of late 2025, the company employs approximately 8,900 to 9,000 personnel and reported annual revenues ranging from $7.5 billion to $8.8 billion. Its market capitalization was around $26 billion in May 2025.
Ameren's core business involves the generation, transmission, and distribution of electricity, as well as the transmission and distribution of natural gas. The company serves approximately 2.4 to 2.5 million electric customers and over 900,000 natural gas customers across a 64,000 to 67,700-square-mile service territory in central and eastern Missouri and central and southern Illinois. Key subsidiaries include Ameren Missouri, Ameren Illinois, Ameren Transmission Company, and Ameren Services. Ameren's generating capacity is approximately 9,300 to 9,700 megawatts.
In patent litigation, Ameren Corp. demonstrates the posture of an operating company defending against assertion suits. The company has been named as a defendant in its sole tracked case and has no record as a plaintiff. This aligns with typical behavior for utilities that are often targets of patent infringement claims related to their operational technologies.
Ameren Corp.'s single tracked case is Midwest Energy Emissions Corp. et al. v. Berkshire Hathaway Energy Company et al., filed in the Southern District of Iowa in July 2024. In this multi-defendant suit, Ameren is among several utility companies accused by Midwest Energy Emissions Corp. (ME2C) of infringing patents related to methods and materials for removing mercury from flue gas in coal-fired power plants. This litigation specifically targets technologies involved in environmental controls for electricity generation.