Washington County (standard abbreviation: WS) is a county located in the U.S. state of Kansas. As of the 2010 census, the county population was 5,799 with a 2018 estimate of 5,420. Its county seat and largest city is Washington.
According to the U.S. Census Bureau, the county has a total area of 899 square miles (2,330 km), of which 895 square miles (2,320 km) is land and 3.9 square miles (10 km) (0.4%) is water.
As of the census of 2000, there were 6,483 people, 2,673 households, and 1,780 families residing in the county. The population density was 7 people per square mile (3/km²). There were 3,142 housing units at an average density of 4 per square mile (1/km²). The racial makeup of the county was 98.90% White, 0.11% Black or African American, 0.34% Native American, 0.05% Asian, 0.09% from other races, and 0.51% from two or more races. 0.65% of the population were Hispanic or Latino of any race.
There were 2,673 households out of which 26.60% had children under the age of 18 living with them, 59.40% were married couples living together, 4.20% had a female householder with no husband present, and 33.40% were non-families. 31.20% of all households were made up of individuals and 17.80% had someone living alone who was 65 years of age or older. The average household size was 2.35 and the average family size was 2.96.
In the county, the population was spread out with 23.70% under the age of 18, 5.40% from 18 to 24, 22.90% from 25 to 44, 23.00% from 45 to 64, and 25.10% who were 65 years of age or older. The median age was 44 years. For every 100 females there were 100.80 males. For every 100 females age 18 and over, there were 97.80 males.
The median income for a household in the county was $29,363, and the median income for a family was $37,260. Males had a median income of $25,074 versus $18,000 for females. The per capita income for the county was $15,515. About 7.30% of families and 10.10% of the population were below the poverty line, including 12.20% of those under age 18 and 12.40% of those age 65 or over.