Barnwell is a city in and county seat of Barnwell County, South Carolina, United States, located along U.S. Route 278. The population was 4,750 at the 2010 census.

Barnwell County is a county in the U.S. state of South Carolina. As of the 2020 census, its population was 20,589. It is located in the Central Savannah River Area. Its county seat is Barnwell.