There are 11 US Post Offices in Richland County serving a total of 15,479 residents equating to 1,407 residents per post office. It's estimated that approximately 24,706 packages are handled across the 11 county post offices annually. Richland County is a county located in the U.S. state of North Dakota. As of the 2010 census, the population was 16,321. Its county seat is Wahpeton. The county was created by the 1872-73 territorial legislature and named for Morgan T. Rich of Wahpeton, who settled on the site of the future city in 1869. County government was organized on November 25, 1873. Richland County is part of the Wahpeton, ND\u2013MN Micropolitan Statistical Area, which is also included in the Fargo-Wahpeton, ND-MN Combined Statistical Area."