Dane County is the second most populous county in Wisconsin behind Milwaukee County. The governing body of Dane County is the Dane County Board of Supervisors.
As of the census of 2000, there were 426,526 people, 173,484 households, and 100,794 families residing in the county. The population density was 355 people per square mile (137/km²). There were 180,398 housing units at an average density of 150 per square mile (58/km²). The racial makeup of the county was 88.96% White, 4.00% Black or African American, 0.33% Native American, 3.45% Asian, 0.03% Pacific Islander, 1.43% from other races, and 1.79% from two or more races. 3.37% of the population were Hispanic or Latino of any race. 34.4% were of German, 11.5% Norwegian, 8.9% Irish and 6.0% English ancestry according to Census 2000.
There were 173,484 households out of which 29.00% had children under the age of 18 living with them, 47.10% were married couples living together, 7.90% had a female householder with no husband present, and 41.90% were non-families. 29.40% of all households were made up of individuals and 7.00% had someone living alone who was 65 years of age or older. The average household size was 2.37 and the average family size was 2.97.
In the county, the population was spread out with 22.60% under the age of 18, 14.30% from 18 to 24, 32.50% from 25 to 44, 21.30% from 45 to 64, and 9.30% who were 65 years of age or older. The median age was 33 years. For every 100 females there were 97.90 males. For every 100 females age 18 and over, there were 96.00 males.