Charleston County is located in the U.S. state of South Carolina along the Atlantic coast. As of the 2020 census, the population was 408,235, making it the third-most populous county in South Carolina. Its county seat is Charleston. It is also the largest county in the state by total area, although Horry County has a larger land area. The county was created in 1800 by an act of the South Carolina State Legislature.

The Charleston metropolitan area is an urban area centered around Charleston, South Carolina. The U.S. Office of Management and Budget designates the area as the Charleston-North Charleston, SC Metropolitan Statistical Area, a metropolitan statistical area used for statistical purposes only by the United States Census Bureau and other federal agencies. The OMB defines the area as comprising Berkeley, Charleston and Dorchester counties, an area with 799,636 residents in the 2020 census. Principal cities include Charleston, North Charleston, and Summerville. The area is commonly referred to as the Tri-County Area or the Lowcountry, though the latter term has historically referred to South Carolina's southern coast in general.