As of the census of 2000, there were 19,526 people, 7,059 households, and 4,990 families residing in the county. The population density was 46 people per square mile (18/km²). There were 7,427 housing units at an average density of 18 per square mile (7/km²). The racial makeup of the county was 94.65% White, 2.26% Black or African American, 0.59% Native American, 0.46% Asian, 0.03% Pacific Islander, 1.29% from other races, and 0.71% from two or more races. 2.90% of the population were Hispanic or Latino of any race. 47.6% were of German, 15.5% Norwegian, 7.4% Irish and 5.5% American ancestry according to Census 2000.
There were 7,059 households out of which 34.70% had children under the age of 18 living with them, 59.00% were married couples living together, 7.80% had a female householder with no husband present, and 29.30% were non-families. 25.10% of all households were made up of individuals and 10.70% had someone living alone who was 65 years of age or older. The average household size was 2.56 and the average family size was 3.07.
In the county the population was spread out with 25.80% under the age of 18, 8.70% from 18 to 24, 30.00% from 25 to 44, 21.30% from 45 to 64, and 14.20% who were 65 years of age or older. The median age was 36 years. For every 100 females there were 109.30 males. For every 100 females age 18 and over, there were 111.30 males.
The median income for a household in the county was $42,440, and the median income for a family was $50,081. Males had a median income of $34,380 versus $22,630 for females. The per capita income for the county was $18,631. About 4.50% of families and 6.50% of the population were below the poverty line, including 8.80% of those under age 18 and 5.80% of those age 65 or over.