As of the census of 2000, there were 55,941 people, 21,062 households, and 12,616 families residing in the county. The population density was 74 people per square mile (29/km²). There were 21,971 housing units at an average density of 29 per square mile (11/km²). The racial makeup of the county was 94.96% White, 1.19% Black or African American, 0.28% Native American, 1.79% Asian, 0.06% Pacific Islander, 0.69% from other races, and 1.03% from two or more races. 1.77% of the population were Hispanic or Latino of any race. 47.6% were of German, 13.6% Norwegian and 6.5% Irish ancestry according to Census 2000.
There were 21,062 households out of which 29.10% had children under the age of 18 living with them, 48.60% were married couples living together, 7.80% had a female householder with no husband present, and 40.10% were non-families. 27.10% of all households were made up of individuals and 9.50% had someone living alone who was 65 years of age or older. The average household size was 2.46 and the average family size was 2.99.
In the county the population was spread out with 21.40% under the age of 18, 22.10% from 18 to 24, 25.60% from 25 to 44, 18.80% from 45 to 64, and 12.10% who were 65 years of age or older. The median age was 30 years. For every 100 females there were 99.10 males. For every 100 females age 18 and over, there were 97.40 males.
The median income for a household in the county was $38,940, and the median income for a family was $50,257. Males had a median income of $32,087 versus $22,527 for females. The per capita income for the county was $18,712. About 6.10% of families and 12.90% of the population were below the poverty line, including 10.50% of those under age 18 and 9.40% of those age 65 or over.