There are 5 US Post Offices in Mountrail County serving a total of 7,823 residents equating to 1,565 residents per post office. It's estimated that approximately 12,486 packages are handled across the 5 county post offices annually. Mountrail County is a county located in the U.S. state of North Dakota. As of the 2010 census, the population was 7,673. Its county seat is Stanley. The county was originally created in 1873, then removed in 1892 and re-created and organized in 1909."