Barnesville is a city in Lamar County, Georgia, United States. As of the 2010 census, the city had a population of 6,755, up from 5,972 at the 2000 census. The city is the county seat of Lamar County and is just outside of the Atlanta metropolitan area. Barnesville is located 37 miles northwest of Macon and 60 miles south of Atlanta. It was called the "Buggy Capital of the South", as the town produced about 9,000 buggies a year around the turn of the 20th century.