As of the census of 2000, there were 66,533 persons, 26,819 households, and 17,754 families residing in the county. The population density was 12 people per square mile (5/km²). There were 29,882 housing units at an average density of 6 per square mile (2/km²). The racial makeup of the county was 94.15% White, 0.76% Black or African American, 1.03% Native American, 0.42% Asian, 0.04% Pacific Islander, 1.92% from other races, and 1.68% from two or more races. 4.90% of the population were Hispanic or Latino of any race. 24.6% were of German, 11.6% English, 11.3% American and 11.2% Irish ancestry according to Census 2000.
There were 26,819 households out of which 32.20% had children under the age of 18 living with them, 51.40% were married couples living together, 10.60% had a female householder with no husband present, and 33.80% were non-families. 27.50% of all households were made up of individuals and 9.40% had someone living alone who was 65 years of age or older. The average household size was 2.42 and the average family size was 2.95.
In the county the population was distributed as follows: 26.00% under the age of 18, 10.10% from 18 to 24, 27.90% from 25 to 44, 23.30% from 45 to 64, and 12.70% who were 65 years of age or older. The median age was 36 years. For every 100 females there were 97.70 males. For every 100 females age 18 and over, there were 95.00 males.
The median income for a household in the county was $36,619, and the median income for a family was $45,575. Males had a median income of $33,524 versus $21,374 for females. The per capita income for the county was $18,913. About 8.70% of families and 11.80% of the population were below the poverty line, including 16.20% of those under age 18 and 7.20% of those age 65 or over.