Dillon County is a county located in the U.S. state of South Carolina. As of the 2010 census, the county's population was 32,062. The county seat is Dillon. Founded in 1910 from a portion of Marion County, both Dillon County and the city of Dillon were named for prosperous local citizen James W. Dillon (1826-1913), an Irishman who settled there and led a campaign to bring the railroad into the community.