Decatur County (county code DC) is a county located in Northwest Kansas. As of the 2010 census, the county population was 2,961. Its county seat and most populous city is Oberlin. The county is named in honor of Commodore Stephen Decatur, Jr.
According to the U.S. Census Bureau, the county has a total area of 894 square miles (2,320 km), of which 894 square miles (2,320 km) is land and 0.6 square miles (1.6 km) (0.07%) is water.
As of the 2000 census, there were 3,472 people, 1,494 households, and 981 families residing in the county. The population density was 4 people per square mile (2/km²). There were 1,821 housing units at an average density of 2 per square mile (1/km²). The racial makeup of the county was 97.87% White, 0.52% Black or African American, 0.09% Native American, 0.14% Asian, 0.12% Pacific Islander, 0.37% from other races, and 0.89% from two or more races. Hispanic or Latino of any race were 0.98% of the population.
There were 1,494 households out of which 25.80% had children under the age of 18 living with them, 57.00% were married couples living together, 5.60% had a female householder with no husband present, and 34.30% were non-families. 32.80% of all households were made up of individuals and 17.50% had someone living alone who was 65 years of age or older. The average household size was 2.24 and the average family size was 2.83.
In the county, the population was spread out with 23.60% under the age of 18, 4.70% from 18 to 24, 22.90% from 25 to 44, 22.60% from 45 to 64, and 26.20% who were 65 years of age or older. The median age was 44 years. For every 100 females there were 97.50 males. For every 100 females age 18 and over, there were 91.40 males.
The median income for a household in the county was $30,257, and the median income for a family was $34,982. Males had a median income of $25,139 versus $17,368 for females. The per capita income for the county was $16,348. About 8.00% of families and 11.60% of the population were below the poverty line, including 17.20% of those under age 18 and 6.30% of those age 65 or over.