There are 1 US Post Offices in Slope County serving a total of 132 residents equating to 132 residents per post office. It's estimated that approximately 211 packages are handled across the 1 county post offices annually. Slope County is a county located in the U.S. state of North Dakota. As of the 2010 census, the population was 727, making it the least populous county in North Dakota and the 20th-least populous county in the United States. The county seat is Amidon. The county was created in 1914 when Billings County was subdivided into three new counties; it was organized on January 14, 1915. The name refers to the Missouri Slope, a geographical feature that is also a popular designation for western North Dakota, particularly the area west of the Missouri River."