Lamar County is a county located in the west central portion of the U.S. state of Georgia. The county seat is Barnesville.
Lamar County is included in the Atlanta-Sandy Springs-Roswell, GA Metropolitan Statistical Area.
According to the U.S. Census Bureau, Lamar County has a total area of 186 square miles (480 km2), of which 184 square miles (480 km2) is land and 2.3 square miles (6.0 km2) (1.3%) is water.
The western third of Lamar County, west of a line from Orchard Hill through Milner and Barnesville, is located in the Upper Flint River sub-basin of the ACF River Basin (Apalachicola-Chattahoochee-Flint River Basin). The eastern majority of the county is located in the Upper Ocmulgee River sub-basin of the Altamaha River basin.
