Williamson is a city in Mingo County, West Virginia, United States, along the Tug Fork River. The population was 3,191 at the 2010 census. It is the county seat of Mingo County, and is the county's largest and most populous city. Williamson is home to Southern West Virginia Community and Technical College. The Tug Fork River separates Williamson from South Williamson, Kentucky.Williamson is the site of a large rail yard built by the former Norfolk and Western Railroad, which was built to service the many coal mines of the region. The city is protected by a floodwall, completed by the U.S. Army Corps of Engineers in 1991 in response to devastating floods along the Tug Fork River in 1977 and again in 1984. The wall incorporates floodgates along major access points which, when locked, form a solid barrier against floodwaters.