There are 6 US Post Offices in Mckenzie County serving a total of 4,948 residents equating to 825 residents per post office. It's estimated that approximately 7,898 packages are handled across the 6 county post offices annually. McKenzie County is a county located in the U.S. state of North Dakota. As of the 2010 census, the population was 6,360. Its county seat is Watford City. Between 2010 and 2015, according to Census Bureau estimates, it was the fastest growing county in the United States, growing 101.7 percent. The county lies immediately adjacent to the Williston Micropolitan Statistical Area, although, technically, by Census Bureau definition, is not a part of it. McKenzie County was first created by the March 8, 1883 Dakota Territory legislature but eliminated in 1891 due to a lack of settlement. The county was then recreated by the 1905 state legislature, with the county government first organizing on April 20, 1905. The name comes from early North Dakota politician Alexander McKenzie. Before becoming Watford City, the county seat was Alexander from 1905 to 1907 and Schafer from 1907 to 1941.