Marion County is a county located in the coastal plain of the U.S. state of South Carolina. As of the 2020 census, its population was 29,183. Its county seat is Marion. It is a majority-minority county.

Marion is a city in and the county seat of Marion County, South Carolina, United States. It is named for Francis Marion, a brigadier general from South Carolina in the American Revolutionary War. The population was 6,939 at the 2010 census.