Allendale County is a county located in the U.S. state of South Carolina. As of the 2020 census, the population was 8,039, making it the least populous county in South Carolina. Its county seat is Allendale.

Allendale is a town in and the county seat of Allendale County, South Carolina, United States. The population was 3,482 at the 2010 census, a decline from 4,052 in 2000.