The Truman Reservoir (also known as Truman Lake) is located in the state of Missouri, United States. It is the largest man-made lake in Missouri and the dam that created and manages the lake’s water level. It is located between Clintonand Warsaw, on the Osage River and extends south to Osceola. The dam is located in Benton County, but the reservoir also extends into parts of Henry, St. Clair, and Hickory counties.