Edgefield County is a county located on the western border of the U.S. state of South Carolina. As of the 2020 census, its population was 25,657. Its county seat and largest community is Edgefield. The county was established on March 12, 1785.The Savannah River makes up part of the western border of Edgefield County; across the river lies the city of Augusta, Georgia. Edgefield is part of the Augusta-Richmond County, GA-SC Metropolitan Statistical Area.