As of the 2010 United States Census, there were 39,265 people, 16,241 households, and 10,331 families living in the county. The population density was . There were 17,438 housing units at an average density of . The racial makeup of the county was 90.1% white, 5.6% American Indian, 0.7% Asian, 0.3% black or African American, 0.1% Pacific islander, 0.7% from other races, and 2.5% from two or more races. Those of Hispanic or Latino origin made up 2.8% of the population. In terms of ancestry, 30.6% were German, 14.5% were Irish, 13.5% were English, and 7.7% were American.