county, southern South Carolina, U.S. It is a rural area on the Coastal Plain. The Savannah River border with Georgia defines the western boundary, the Salkehatchie River the northeastern. It is also drained by the Coosawhatchie River. Much of the area is covered by pine and mixed forests. Swamps along the Savannah River valley provide habitat for a variety of wildlife (including alligators), and fishing and hunting for quail and deer have traditionally been popular local attractions.

Watermelons, corn (maize), wheat, and soybeans are the chief agricultural products. Also important to the economy is the manufacture of wood, chemical, and textile products. The county was the last to be established in the state, in 1919. The town of Allendale is the county seat. Both county and town are named for Paul H. Allen, the town's first postmaster. Area 408 square miles (1,057 square km). Pop. (2000) 11,211; (2007 est.) 10,475.