There are 10 US Post Offices in Williams County serving a total of 40,804 residents equating to 4,080 residents per post office. It's estimated that approximately 65,128 packages are handled across the 10 county post offices annually. Williams County is a county located in the U.S. state of North Dakota. As of the 2010 census, the population was 22,398. Its county seat is Williston. Between 2010 and 2015, according to Census Bureau estimates, it was the second-fastest growing county in the United States, trailing only neighboring McKenzie County, to its south. The Williston Micropolitan Statistical Area includes all of Williams County. The Micropolitan Statistical Area is the fastest-growing Primary Statistical Area, growing 57.6% in population from 2010 to 2015. In 2014, Williams County had the lowest percentage of unemployed people of any county in the United States, at 1.2 percent."