At the 2000 census there were 40,066 people, 15,017 households, and 11,022 families in the county. The population density was 16 people per square mile. There were 17,599 housing units at an average density of 7 per square mile. The racial makeup of the county was 90.05% White, 0.28% Black or African American, 5.66% Native American, 0.48% Asian, 0.16% Pacific Islander, 0.68% from other races, and 2.70% from two or more races. 1.84%. were Hispanic or Latino of any race. 20.6% were of German, 18.9% United States or American, 10.0% English, 7.9% Irish and 5.0% Norwegian ancestry. Of the 15,017 households 34.40% had children under the age of 18 living with them, 60.40% were married couples living together, 8.70% had a female householder with no husband present, and 26.60% were non-families. 22.00% of households were one person and 8.80% were one person aged 65 or older. The average household size was 2.64 and the average family size was 3.08. The age distribution was 28.70% under the age of 18, 6.40% from 18 to 24, 24.90% from 25 to 44, 27.10% from 45 to 64, and 12.90% 65 or older. The median age was 39 years. For every 100 females there were 99.10 males. For every 100 females age 18 and over, there were 96.60 males. The median household income was $34,673 and the median family income was $40,250. Males had a median income of $35,256 versus $23,679 for females. The per capita income for the county was $15,895. About 11.50% of families and 15.90% of the population were below the poverty line, including 19.80% of those under age 18 and 11.90% of those age 65 or over.
2010 census
At the 2010 census, the population density was. There were 21,156 housing units at an average density of. The racial makeup of the county was 88.9% White, 0.6% Black or African American, 1.5% Native American, 1.5% Asian, 0.2% Pacific Islander, 3.5% from other races, 3.7% two or more races. Those of Hispanic or Latino origin made up 2.7% of the population. In terms of ancestry, 24.6% were German, 14.2% were Irish, 13.7% were English, 6.4% were Norwegian, and 6.1% were American. Of the households, 29.6% had children under the age of 18 living with them, 56.3% were married couples living together, 9.0% had a female householder with no husband present, 29.9% were non-families, and 24.6% of households were made up of individuals. The average household size was 2.50 and the average family size was 2.95. The median age was 45.0 years. The median household income was $42,845 and the median family income was $51,544. Males had a median income of $46,721 versus $33,651 for females. The per capita income for the county was $21,773. About 11.0% of families and 15.1% of the population were below the poverty line, including 21.1% of those under age 18 and 9.3% of those age 65 or over.
