Ameren Corporation is an American power company created December 31, 1997, by the merger of St. Louis, Missouri's Union Electric Company (formerly NYSE: UEP) and the neighboring Central Illinois Public Service Company (CIPSCO Inc. holding, formerly NYSE: CIP) of Springfield, Illinois. It is now a holding company for several power companies and energy companies. The company is based in St. Louis, serving 2.4 million electric, and 900,000 natural gas customers across 64,000 square miles in central and eastern Missouri and the southern four-fifths of Illinois.