South Williamson is a unincorporated community in the Appalachian Mountains of northeastern Pike County, Kentucky, United States, on the border with West Virginia. It is separated from Williamson, West Virginia by the Tug Fork River. The community is located near U.S. Route 119 about 23 miles east of Pikeville, Kentucky and 28 miles southwest of Logan, West Virginia. For statistical purposes, the United States Census Bureau has defined that community as a census-designated place.