Charleston is the most populous city in the U.S. state of South Carolina. The city lies just south of the geographical midpoint of South Carolina's coastline on Charleston Harbor, an inlet of the Atlantic Ocean formed by the confluence of the Ashley, Cooper, and Wando rivers. Charleston had a population of 150,227 at the 2020 census, while the Charleston metropolitan area, comprising Berkeley, Charleston, and Dorchester counties, has an estimated 870,000 residents. It ranks as the third-most populous metropolitan area in the state and the 71st-most populous in the U.S. It is the county seat of Charleston County.