As of the census of 2000, there were 38,520 people, 15,836 households, and 10,689 families residing in the county. The population density was 33 people per square mile (13/km²). There were 19,223 housing units at an average density of 16 per square mile (6/km²). The racial makeup of the county was 95.83% White, 0.09% Black or African American, 2.21% Native American, 0.31% Asian, 0.03% Pacific Islander, 0.14% from other races, and 1.39% from two or more races. 0.49% of the population were Hispanic or Latino of any race. 15.7% were of French, 15.5% German, 10.9% Swedish, 10.6% French Canadian and 5.8% Irish ancestry. 98.0% spoke English as their first language.
There were 15,836 households out of which 29.7% had children under the age of 18 living with them, 55.8% were married couples living together, 8.3% had a female householder with no husband present, and 32.5% were non-families. 28.0% of all households were made up of individuals and 13.0% had someone living alone who was 65 years of age or older. The average household size was 2.40 and the average family size was 2.93.
In the county the population was spread out with 23.8% under the age of 18, 7.9% from 18 to 24, 26.0% from 25 to 44, 25.4% from 45 to 64, and 17.0% who were 65 years of age or older. The median age was 40 years. For every 100 females there were 96.6 males. For every 100 females age 18 and over, there were 93.6 males.
The median income for a household in the county was $35,511, and the median income for a family was $45,079. Males had a median income of $37,057 versus $22,368 for females. The per capita income for the county was $18,667. About 7.0% of families and 9.5% of the population were below the poverty line, including 10.7% of those under age 18 and 9.2% of those age 65 or over.