Dunn County is a county located in the U.S. state of North Dakota. As of the 2010 census, the population was 3,536. Its county seat is Manning. The county was created by the 1883 Dakota Territory legislature and named for John Piatt Dunn, who opened the first drugstore in North Dakota and was a civic and commercial leader during the early history of Bismarck. The county government was first organized on February 10, 1908.