Williston is a city in and the county seat of Williams County, North Dakota, United States. The 2020 census gave its population as 29,160, maki…Williston is a city in and the county seat of Williams County, North Dakota, United States. The 2020 census gave its population as 29,160, making Williston the sixth-most populous city in North Dakota. The city's population nearly doubled between 2010 and 2020, due largely to the North Dakota oil boom.