As of the 2010 census, there were 21,100 people, 8,931 households, and 5,255 families in the county. The population density was . There were 9,862 housing units at an average density of . The racial makeup of the county was 95.6% white, 1.4% American Indian, 0.7% black or African American, 0.5% Asian, 0.1% Pacific islander, 0.5% from other races, and 1.3% from two or more races. Those of Hispanic or Latino origin made up 1.7% of the population. In terms of ancestry, 56.5% were German, 27.6% were Norwegian, 7.2% were Irish, 6.0% were Russian, 5.2% were English, and 2.4% were American.