Lydia is an unincorporated community and census-designated place in Darlington County, South Carolina, United States. As of the 2010 census, the population of the CDP was 642. It is the location of Lydia Plantation, which is listed on the U.S. National Register of Historic Places. Lydia is in western Darlington County, just east of the Lee County line. U.S. Route 15 passes through the community, leading northeast 7 miles to Hartsville and southwest 10 miles to Bishopville.