county, central South Carolina, U.S. It consists of a low-lying region on the Coastal Plain that includes large areas of swampland. Lake Marion, formed by the Santee Dam on the Santee River (Santee-Wateree-Catawba river system), constitutes the western and southern border, and the county is also drained by the Black River. Santee National Wildlife Refuge is on Lake Marion, a popular attraction for fishing enthusiasts. At the northern tip of Clarendon county is Woods Bay State Park, featuring a large Carolina bay (an isolated swampy area) inhabited by alligators.

Congaree Indians lived in the region in the late 17th century. During the U.S. War of Independence (American Revolution) three skirmishes occurred in the area. The county was established in 1785 and named for Edward Hyde, 3rd earl of Clarendon.

Much of the region is covered by pine and hardwood forests. Logging and lumber mills, along with the manufacture of clothing, are important elements of the economy. Tobacco, soybeans, chickens, and hogs are the chief products of the county's flourishing farms. Manning is the county seat. Area 607 square miles (1,573 square km). Pop. (2000) 32,502; (2007 est.) 32,822.