As of the census of 2000, there were 52,468 people, 20,439 households, and 14,164 families residing in the county. The population density was 68 people per square mile. There were 22,685 housing units at an average density of 29 per square mile. The racial makeup of the county was 97.18% White, 0.88% Black or African American, 0.35% Native American, 0.33% Asian, 0.02% Pacific Islander, 0.44% from other races, and 0.79% from two or more races. 1.58% of the population were Hispanic or Latino of any race. 46.4% were of German, 10.2% Norwegian, 7.8% Irish, 6.4% English and 5.0% United States or American ancestry. There were 20,439 households out of which 32.20% had children under the age of 18 living with them, 58.10% were married couples living together, 7.40% had a female householder with no husband present, and 30.70% were non-families. 25.50% of all households were made up of individuals and 11.00% had someone living alone who was 65 years of age or older. The average household size was 2.49 and the average family size was 2.99. In the county, the population was spread out with 25.20% under the age of 18, 7.10% from 18 to 24, 29.90% from 25 to 44, 23.40% from 45 to 64, and 14.40% who were 65 years of age or older. The median age was 38 years. For every 100 females, there were 101.60 males. For every 100 females age 18 and over, there were 100.40 males. In 2017, there were 602 births, giving a general fertility rate of 63.9 births per 1000 women aged 15–44, the 35th highest out of all 72 Wisconsin Counties. Additionally, there were 63 reported induced abortions performed on women of Columbia County residence, with a rate of 6.7 abortions per 1000 women aged 15–44, which is above the Wisconsin average rate of 5.2.
For most of its history, Columbia County voters have backed the Republican Party candidate in national elections. Prior to 1992, the only times Republicans failed to win the county in the preceding 100 years of presidential elections were in the midst of a divided party vote in 1912, in 1924 when Wisconsinite Robert La Follette was on the ballot, and in the national Democratic Party landslides of 1932, 1936, & 1964. From 1992 onward, the county has been a Democratic-leaning swing county, voting for the statewide winner in all presidential elections since then except in 2004, and voting for the national winner in all except 2000. Republican Donald Trump won the county in 2016, though a majority of county residents voted for Democrat Tammy Baldwin's re-election to the U.S. Senate two years later in 2018.
