Williamstown is a city in Wood County, West Virginia, United States, along the Ohio River. It is part of the Parkersburg-Marietta-Vienna metropolitan area. The population was 2,908 at the 2010 census. The now closed Fenton Art Glass Company was located in the city.
Williamstown was named for Isaac Williams (1737–1820), who settled here in 1787. Williams had served under General Braddock (1755) as a ranger and spy and under Governor Dunmore (1774) fighting against the Shawnee. His home was on 400 acres on the Ohio River opposite the mouth of the Muskingum River, site of Marietta, Ohio, which was founded about a year after he arrived. Other local namesakes include Williams Creek and Williams District. The settlement was known as "Williamsport" to Ohio River travelers until 1822 when the present name was formalized.
Located in Williamstown is the Tomlinson Mansion, listed on the National Register of Historic Places in 1974.