Williamson, the county seat of Mingo County, is located on the Tug Fork of the Big Sandy River at the junction of U.S. 119 (Appalachian Corridor G) and U.S. 52. The town is situated on the state line, just across the river from South Williamson, Kentucky, and in the heart of the rich bi-state Williamson Coalfield. The Norfolk Southern Railroad runs through Williamson, which has a major rail yard.

Williamson was named for the prominent Williamson family and established on land belonging to them. The site was still farmland as late as 1890, but was transformed as the Norfolk & Western Railway (now Norfolk Southern) built its main line through the area. The county seat was located there when Mingo County was created in 1895, due to the influence of the Williamsons and other local backers. Matewan, upstream on the Tug Fork and also on the N&W line, challenged Williamson for the county seat as early as 1896. The unsuccessful bid marked the beginning of a long-term rivalry between the two towns, which are Mingo County's largest communities.

Incorporated in 1905, Williamson boomed with the growth of Mingo County and the development of the local coalfields. The city's population peaked at 8,624 in 1950. Thereafter, Williamson lost population with the decline of mining employment and the loss of railroad jobs that accompanied the shift from steam to diesel power. Williamson's population was 3,191 in 2010.

Williamson was once the victim of periodic flooding by the Tug Fork. On April 5, 1977, the Tug reached a record 52.56 feet, more than 25 feet above flood stage. In 1991, a floodwall was constructed to protect the town.

The Coal House, a downtown landmark built of bituminous coal in 1933, was added to the National Register of Historic Places in 1980. The Williamson Historic District was added to the National Register in 2006.

Read the National Register of Historic Places nomination for the Williamson Historic District.