The 148-foot (45 m) tall concrete gravity dam was built by the Union Electric Company (now Ameren) to generate hydroelectric power at its Osage Powerplant.

The concept of a hydro-electric power plant on the Osage River was first introduced by a Kansas City developer as early as 1912.

Union Electric Power and Light stepped in with engineering firm Stone & Webster from Boston, Massachusetts.

[10] The stock market crash of 1929, which precipitated the Great Depression, occurred just months after construction on Bagnell Dam began.

The project employed thousands of laborers, providing a large economic boost to the rural area around the dam and to the state as a whole at a time when jobs were scarce.

In 2017, a major structural project began to add a new series of anchors and concrete on the downstream side of the dam.

The structure on top was in much poorer condition causing more work to be needed and an 18-ton weight limit was posted once the bridge reopened to traffic.

[15] Ameren remotely operates the Taum Sauk pumped storage plant from its control room at Bagnell Dam.