High Quality Content by WIKIPEDIA articles! Ameren Corporation was created December 31, 1997 by the merger of Missouri`s Union Electric Company (formerly NYSE: UEP) and the neighboring Central Illinois Public Service Company (CIPSCO Inc. holding, formerly NYSE: CIP). It is now a holding company for several power companies and energy companies. The company is based in St. Louis, Missouri, serving 2.4 million electric, and 900,000 natural gas customers across 64,000 sq. mi.