"Union Electric Company was incorporated in Missouri in 1922 as Union Electric Light and Power Company, a successor to a company of the same name incorporated in May 1902 as a result of the merger of Imperial Electric Light, Heat and Power Company, Citizens Electric Lighting and Power Company, and Missouri Edison Electric Company. An early project for Union Electric Light and Power was providing power for the St. Louis World’s Fair of 1904.
As individuals and businesses began to rely more on electricity and as demand increased, Union Electric sought additional generating sources. In 1913 it began buying power from the Keokuk dam, 150 miles north of St. Louis. During World War I, the company expanded to serve rural areas. With the addition of a plant in Cahokia, Illinois, Union Electric progressed through the 1920s, acquiring smaller light and power companies in Missouri and Illinois.
In the early 1930s, despite the Great Depression, Union Electric completed construction of Bagnell dam in Missouri’s Ozark Mountains and organized Lakeside Light & Power Company for residents in the surrounding area. The company changed its name to Union Electric Company of Missouri in 1937. Its Illinois operations became a subsidiary, Union Electric Company of Illinois, with subsidiaries in Iowa renamed Iowa Union Electric Company. The company proceeded with further corporate streamlining in 1940, merging several Missouri subsidiaries into the parent. Surrounding Illinois and Iowa properties were merged into one subsidiary, Union Electric Power Company, by 1945. In March 1945 Union Electric made the significant acquisition of Laclede Power & Light Company, a former competitor controlling 15 percent of the electric business in St. Louis.
After World War II, Union Electric continued its history of expanding through building and acquisitions. In 1950 it completed a new plant in Venice, Illinois, bringing the total capacity to 1,000 megawatts. It acquired Missouri Power & Light Company in 1950, followed by the 1954 purchase of Missouri Edison Company. In February 1955 Union Electric absorbed its holding company, North American Company, and in August 1955 purchased all properties and on-going businesses in Illinois and Iowa of the subsidiary, Union Electric Power Company. Following this consolidation in 1956, Union Electric Company of Missouri became simply Union Electric Company. The company made one more electric company acquisition in southeastern Iowa in 1958.
Union Electric began construction of intercompany transmission lines in the early 1950s, establishing power pools that any unit connected to the system could access. Soon outside companies joined the power pool, bringing the total number of utilities to seventeen.
In the early 1960s approximately 75 percent of Union Electric’s business was providing electricity to St. Louis. The city’s increasing demand for power was evidenced by the addition of a new expressway, civic center, sports stadium, and several new office and apartment complexes.
In 1965 Union Electric extended its reach in generation, transmission, and interconnection by joining with six other utilities to pool resources in Mid-Continent Area Power Planners. The member area reached from St. Louis north to St. Paul, Minnesota."