2000 - 54,544 1990 - 39,413 1980 - 37,202 1970 - 26,374 1960 - 17,540 1950 - 12,115 1940 - 11,105 1930 - 10,555 1920 - 10,074 1910 - 10,777 1900 - 11,467 1890 - 12,106 1880 - 13,083 1870 - 12,399 1860 - 13,074 1850 - 7,730
As of the census of 2000, there were 54,544 people, 18,798 households, and 14,963 families residing in the county. The population density was 170 people per square mile (66/km²). There were 19,519 housing units at an average density of 61 per square mile (24/km²). The racial makeup of the county was 92.88% White, 1.32% Black or African American, 0.19% Native American, 0.88% Asian, 0.02% Pacific Islander, 3.38% from other races, and 1.34% from two or more races. 7.49% of the population were Hispanic or Latino of any race. 27.2% were of German, 12.5% Irish, 7.4% English, 5.9% Polish, 5.8% Norwegian, 5.1% American and 5.0% Italian ancestry according to Census 2000. 91.6% spoke English and 6.5% Spanish as their first language.
There were 18,798 households out of which 41.70% had children under the age of 18 living with them, 68.80% were married couples living together, 7.50% had a female householder with no husband present, and 20.40% were non-families. 16.40% of all households were made up of individuals and 6.10% had someone living alone who was 65 years of age or older. The average household size was 2.89 and the average family size was 3.27.
In the county the population was spread out with 29.50% under the age of 18, 7.50% from 18 to 24, 32.40% from 25 to 44, 22.10% from 45 to 64, and 8.50% who were 65 years of age or older. The median age was 34 years. For every 100 females there were 98.70 males. For every 100 females age 18 and over, there were 95.90 males.
The median income for a household in the county was $64,625, and the median income for a family was $69,383 (these figures had risen to $74,539 and $81,517 respectively as of a 2007 estimate). Males had a median income of $50,268 versus $30,415 for females. The per capita income for the county was $25,188. About 2.00% of families and 3.00% of the population were below the poverty line, including 3.50% of those under age 18 and 4.50% of those age 65 or over.