According to the U.S. Census Bureau, the county has a total area of, of which is land and is water. It is part of the Palouse, a wide and rolling prairie-like region of the middleColumbia basin.
As of the census of 2000, there were 4,064 people, 1,687 households, and 1,138 families living in the county. The population density was 5 people per square mile. There were 2,018 housing units at an average density of 2 per square mile. The racial makeup of the county was 93.73% White, 0.22% Black or African American, 0.96% Native American, 0.42% Asian, 0.05% Pacific Islander, 2.73% from other races, and 1.89% from two or more races. 6.35% of the population were Hispanic or Latino of any race. 19.6% were of German, 18.2% United States or American, 14.3% English and 8.3% Irish ancestry. 94.3% spoke English and 5.7% Spanishat home. There were 1,687 households out of which 27.70% had children under the age of 18 living with them, 56.00% were married couplesliving together, 8.50% had a female householder with no husband present, and 32.50% were non-families. 29.00% of all households were made up of individuals and 13.00% had someone living alone who was 65 years of age or older. The average household size was 2.36 and the average family size was 2.89. In the county, the population was spread out with 23.90% under the age of 18, 7.00% from 18 to 24, 22.80% from 25 to 44, 27.70% from 45 to 64, and 18.50% who were 65 years of age or older. The median age was 42 years. For every 100 females there were 95.20 males. For every 100 females age 18 and over, there were 94.80 males. The median income for a household in the county was $33,500, and the median income for a family was $44,038. Males had a median income of $33,690 versus $21,367 for females. The per capita income for the county was $17,374. About 8.60% of families and 12.60% of the population were below the poverty line, including 15.90% of those under age 18 and 11.10% of those age 65 or over.
2010 census
As of the 2010 United States Census, there were 4,078 people, 1,762 households, and 1,156 families living in the county. The population density was. There were 2,136 housing units at an average density of. The racial makeup of the county was 93.0% white, 1.4% American Indian, 0.6% Asian, 0.3% Pacific islander, 0.3% black or African American, 1.7% from other races, and 2.7% from two or more races. Those of Hispanic or Latino origin made up 6.2% of the population. In terms of ancestry, 24.7% were German, 18.3% were English, 12.3% were Irish, and 7.0% were American. Of the 1,762 households, 24.7% had children under the age of 18 living with them, 52.6% were married couples living together, 9.2% had a female householder with no husband present, 34.4% were non-families, and 29.3% of all households were made up of individuals. The average household size was 2.27 and the average family size was 2.76. The median age was 48.3 years. The median income for a household in the county was $43,611 and the median income for a family was $53,452. Males had a median income of $45,000 versus $35,357 for females. The per capita income for the county was $25,810. About 9.8% of families and 16.4% of the population were below the poverty line, including 19.7% of those under age 18 and 10.9% of those age 65 or over.
Communities
City
Dayton
Town
Starbuck
Unincorporated communities
Alto
Huntsville
Marengo
Turner
Politics
Columbia County is one of the most conservative counties in Washington state. It has not been carried by a Democrat for President since Lyndon Johnson's 1964 landslide victory, and the last time it backed a Democrat for Governor was in 1936 when Clarence D. Martin swept every county in the state. Popular conservative Democratic Senator "Scoop" Jackson carried the county in four consecutive county sweeps ; since then, however, it has been powerfully Republican in those contests too.
