As of the census of 2000, there were 16,673 people, 6,457 households, and 4,255 families residing in the county. The population density was 6 people per square mile (2/km²). There were 7,453 housing units at an average density of 3 per square mile (1/km²). The racial makeup of the county was 79.55% White, 0.09% Black or African American, 17.30% Native American, 0.37% Asian, 0.02% Pacific Islander, 0.35% from other races, and 2.32% from two or more races. 1.25% of the population were Hispanic or Latino of any race. 21.1% were of German, 13.5% Norwegian, 8.7% Irish, 6.7% American and 6.2% English ancestry according to Census 2000. 93.9% spoke English, 3.3% Cree and 2.0% German as their first language.
There were 6,457 households out of which 34.30% had children under the age of 18 living with them, 50.50% were married couples living together, 10.90% had a female householder with no husband present, and 34.10% were non-families. 28.60% of all households were made up of individuals and 11.40% had someone living alone who was 65 years of age or older. The average household size was 2.53 and the average family size was 3.15.
In the county the population was spread out with 28.20% under the age of 18, 11.60% from 18 to 24, 26.00% from 25 to 44, 21.40% from 45 to 64, and 12.80% who were 65 years of age or older. The median age was 34 years. For every 100 females there were 99.30 males. For every 100 females age 18 and over, there were 96.40 males.
The median income for a household in the county was $30,781, and the median income for a family was $38,179. Males had a median income of $29,908 versus $19,874 for females. The per capita income for the county was $14,935. About 15.30% of families and 18.40% of the population were below the poverty line, including 23.30% of those under age 18 and 9.00% of those age 65 or over.