Colleton County is a county located in the U.S. state of South Carolina. As of the 2010 census, its population was 38,892. Its county seat is Walterboro. It is named after Sir John Colleton, 1st Baronet, one of the eight Lords Proprietor of the Province of Carolina.

In 1682 Colleton was created as one of the three original proprietary counties, located in the southwestern coastal portion of the new South Carolina Colony, bordering on the Combahee River. In 1706 the county was divided between the new Saint Bartholomew’s and Saint Paul’s Parishes. In 1734 most of the coastal portion of Saint Paul’s Parish was separated to form the new Saint John’s Colleton Parish. In 1769 the three parishes were absorbed into the Charleston Judicial District, the southwestern portion of which was referred to as Saint Bartholomew’s.

In 1800 the new Colleton District was formed from the western half of the Charleston District. In 1816 it annexed a small portion of northwestern Charleston District.

In 1868, under the revised state constitution, South Carolina districts became counties, with officials elected by the resident voters rather than by state officials as done previously.

In 1897 the northeastern portion of the county was separated to form the new Dorchester County, with its seat at Saint George. In 1911 the portion of the county east of the Edisto River was annexed to Charleston County. In 1919 and again in 1920, tiny portions of northwestern Colleton County were annexed to Bamberg County, thus bringing the county down to its present size.