2000 census
As of the census [15] of 2000, there were 20,336 people, 7,626 households, and 5,269 families residing in the county. The population density was 47 people per square mile (18 people/km2). There were 8,246 housing units at an average density of 19 units per square mile (7.3 units/km2). The racial makeup of the county was 94.78% White, 1.49% Black or African American, 0.24% Native American, 1.88% Asian, 0.02% Pacific Islander, 0.52% from other races, and 1.07% from two or more races. 1.26% of the population were Hispanic or Latino of any race.
There were 7,626 households, out of which 32.80% had children under the age of 18 living with them, 57.70% were married couples living together, 8.20% had a female householder with no husband present, and 30.90% were non-families. 26.80% of all households were made up of individuals, and 12.20% 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 2.98.
In the county, the population was spread out, with 24.70% under the age of 18, 9.00% from 18 to 24, 29.20% from 25 to 44, 22.50% from 45 to 64, and 14.70% who were 65 years of age or older. The median age was 37 years. For every 100 females there were 102.50 males. For every 100 females age 18 and over, there were 102.80 males.
The median income for a household in the county was $39,087, and the median income for a family was $46,985. Males had a median income of $31,801 versus $23,075 for females. The per capita income for the county was $18,192. About 6.70% of families and 8.80% of the population were below the poverty line, including 10.30% of those under age 18 and 9.30% of those age 65 or over.
United States
Iowa 
