Williston, city (1990 pop. 13,131), seat of Williams co., NW N.Dak., on the Missouri River; inc. 1904. An early riverboating town, its importance increased with the arrival of the Great Northern Railway (1887) and later by the discovery (1951) of rich oil reserves in the Williston Basin. It is the trade, processing, and shipping center of a spring-wheat and livestock region, with an oil refinery, stockyards, grain elevators, and dairy-processing plants. Huge reserves of lignite, as well as natural gas and salt are in the area. Of interest are the Frontier Museum and nearby Fort Union Trading Post National Historic Site and Fort Buford State Historic Site.