2000 41,335 1990 37,730 1980 36,523 1970 33,187 1960 30,556 1950 28,237 1940 26,612 1930 23,731 1920 24,228 1910 24,727 1900 26,633 1890 24,139 1880 23,050 1870 18,974 1860 16,286 1850 11,047 1840 8,961 1830 4,870 1820 4,010
As of the census of 2000, there were 41,335 people, 16,052 households, and 11,573 families residing in the county. The population density was 81 people per square mile (31/km²). There were 17,137 housing units at an average density of 34 per square mile (13/km²). The racial makeup of the county was 96.13% White, 0.55% Black or African American, 0.24% Native American, 0.78% Asian, 0.06% Pacific Islander, 1.54% from other races, and 0.70% from two or more races. 2.69% of the population were Hispanic or Latino of any race. 33.7% were of American, 30.6% German, 8.1% English and 7.9% Irish ancestry according to Census 2000.
There were 16,052 households out of which 33.70% had children under the age of 18 living with them, 58.10% were married couples living together, 9.90% had a female householder with no husband present, and 27.90% were non-families. 23.50% of all households were made up of individuals and 10.10% had someone living alone who was 65 years of age or older. The average household size was 2.54 and the average family size was 2.98.
In the county the population was spread out with 25.50% under the age of 18, 8.80% from 18 to 24, 30.30% from 25 to 44, 22.10% from 45 to 64, and 13.30% who were 65 years of age or older. The median age was 36 years. For every 100 females there were 97.30 males. For every 100 females age 18 and over, there were 94.60 males.
The median income for a household in the county was $39,401, and the median income for a family was $45,210. Males had a median income of $31,505 versus $22,301 for females. The per capita income for the county was $18,400. About 6.50% of families and 8.50% of the population were below the poverty line, including 9.70% of those under age 18 and 9.00% of those age 65 or over.