From its settlement until the 1930s, the county was nearly completely agricultural.
The creation of Kentucky Lake by the Tennessee Valley Authority in the 1940s brought tourism and industry to the county with resorts along the lake. The Kentucky Dam's cheap and plentiful electricity also attracted chemical and manufacturing plants, mostly in the Calvert City area. The creation of the lake led to the destruction of two Marshall County towns: Birmingham, located about six miles north of the present day town of Fairdealing, and Gilbertsville, which was at the present-day dam site. Gilbertsville was rebuilt somewhat to the west of its original location. Birmingham residents were dispersed. Gilbertsville was an incorporated town until the 1970s, when its charter was dissolved by public vote. Kentucky Lake (created by the impounding of the Tennessee River) and Lake Barkley (created through the impounding of the Cumberland River) make up one of the largest man-made bodies of water in the world.
