Calhoun County is a county in the U.S. state of South Carolina. As of the 2020 census, its population was 14,119, making it the fourth-least populous county in the state. Its county seat is St. Matthews. In terms of land area, it is also the smallest county in the state. Located in a rural upland area long devoted to cotton plantations, part of the Black Belt of the South, the county was formed in 1908 from portions of Lexington and Orangeburg counties. It is named for John C. Calhoun, the former U.S. vice-president, Senator, Representative and cabinet member from South Carolina, although Calhoun was from nearby Abbeville, South Carolina.