Union Electric Co. d/b/a Ameren Missouri, commonly known as Ameren Missouri, is a major electric and natural gas utility based in St. Louis, Missouri. Originally organized in 1902 as Union Electric Company and incorporated in Missouri in 1922, it became a subsidiary of Ameren Corporation in 1997 following the merger of Union Electric Company and CIPSCO Inc. Ameren Corporation is a publicly traded company on the New York Stock Exchange (NYSE: AEE), with approximately 8,913 to 9,244 employees across its operations as of 2025/2026. Ameren Missouri itself employs over 4,000 people. The parent company, Ameren Corporation, reported revenues of approximately $8.80 billion USD in the last fiscal year, with Ameren Missouri contributing $4.76 billion USD to that total.
Ameren Missouri operates as a rate-regulated utility, providing electric generation, transmission, and distribution services, as well as natural gas distribution, across central and eastern Missouri. It serves approximately 1.3 million electric customers and 135,000 natural gas customers in its service territory. The company generates electricity from a diverse portfolio of sources, including coal, nuclear, natural gas, hydroelectric, and solar energy centers.
In terms of patent litigation, Union Electric Co. d/b/a Ameren Missouri's posture is that of an operating company defending against patent assertions. The company has been named as a defendant in all three of its tracked patent litigation cases and has not initiated any suits as a plaintiff. These cases are venued in the U.S. District Court for the Eastern District of Missouri and the U.S. District Court for the Southern District of Iowa, which are not typically identified as plaintiff-friendly patent venues.
All three tracked cases, including "Midwest Energy Emissions Corp. et al. v. MidAmerican Energy Company et al." and "Midwest Energy Emissions Corp. v. Ameren Corp. et al.", name Ameren Missouri as a defendant. The plaintiff in these suits is Midwest Energy Emissions Corp. (ME2C), an entity known for asserting patents related to mercury and particulate emission reduction technologies used in coal-fired power plants. These cases appear to be part of a broader, multi-defendant patent enforcement campaign by ME2C, with some related cases being consolidated into MDL No. 3132. Midwest Energy Emissions Corp. notably secured a $57 million patent infringement verdict in March 2024 in a separate case in the U.S. District Court for the District of Delaware, involving its mercury-capture technologies.