2000 16,577 1990 16,119 1980 16,819 1970 16,650 1960 15,856 1950 15,566 1940 15,135 1930 15,208 1920 16,152 1910 17,459 1900 19,116 1890 18,157 1880 14,407 1870 11,953 1860 8,170 1850 3,532
As of the census of 2000, there were 16,577 people, 6,469 households, and 4,748 families residing in the county. The population density was 64 people per square mile (25/km²). There were 6,848 housing units at an average density of 26 per square mile (10/km²). The racial makeup of the county was 98.35% White, 0.14% Black or African American, 0.22% Native American, 0.30% Asian, 0.01% Pacific Islander, 0.33% from other races, and 0.65% from two or more races. 1.21% of the population were Hispanic or Latino of any race. 33.1% were of American, 22.8% German, 12.7% English and 7.3% Irish ancestry according to Census 2000.
There were 6,469 households out of which 32.50% had children under the age of 18 living with them, 62.30% were married couples living together, 7.70% had a female householder with no husband present, and 26.60% were non-families. 23.10% of all households were made up of individuals and 11.20% had someone living alone who was 65 years of age or older. The average household size was 2.53 and the average family size was 2.97.
In the county the population was spread out with 25.00% under the age of 18, 7.20% from 18 to 24, 28.10% from 25 to 44, 25.10% from 45 to 64, and 14.50% who were 65 years of age or older. The median age was 38 years. For every 100 females there were 95.70 males. For every 100 females age 18 and over, there were 91.60 males.
The median income for a household in the county was $48,546, and the median income for a family was $56,080. Males had a median income of $42,109 versus $25,061 for females. The per capita income for the county was $21,926. About 2.90% of families and 5.10% of the population were below the poverty line, including 4.50% of those under age 18 and 8.80% of those age 65 or over.