In the years after World War II, much of Union Electric's growth came from a number of acquisitions:

Missouri Power & Light Company became a UE subsidiary.

UE gained 40,000 customers when Laclede Gas Company sold its electric utilities in 1945.

In 1950, Missouri Power & Light Company, serving central Missouri, became a wholly owned subsidiary.

Missouri Edison Company joined as an operating subsidiary in 1954, while Missouri Utilities Company became a UE subsidiary in 1974.

On Dec. 30, 1983, these three subsidiaries merged into Union Electric Company.

With the acquisitions came new customers, adding to the growing need for electrical service. In the 1960s and 70s, five new plants began producing power for Union Electric customers, including what was the world's largest coal-fired plant at the time - the 2,400-megawatt Labadie Plant, completed in 1971.

In its early years, Labadie Plant was the world's largest coal-fired plant.

To provide even greater focus to its market area, UE in 1992 acquired the Missouri retail properties of Arkansas Power & Light Company. This acquisition brought 26,000 new electric customers from southeastern Missouri into UE's fold. The same year, UE sold its Iowa and northern Illinois retail properties to other utility companies.