Mableton is a census-designated place in Cobb County, Georgia, United States. As of the 2010 census, Mableton had a population of 37,115. When Brookhaven became a city in December 2012, Mableton became the largest unincorporated community in Metro Atlanta.It was named for Robert Mable, who on September 11, 1843 bought 300 acres (about 120 hectares or 1.2 km²) of land.