Barnesville is a city in Lamar County, Georgia, United States. The population was 5,972 at the 2000 census, making it the most populated city named Barnesville in the United States. The city is the county seat of Lamar County. Barnesville was once dubbed the "Buggy Capital of the World" as the town produced about 16,000 buggies a year around the turn of the century. Each year in the third week of September the town hosts an annual Buggy Days celebration.