Douglas County is a county located in the U.S. state of Illinois. As of the 2010 United States Census, the population was 19,980. The county seat is Tuscola.
According to the US Census Bureau, the county has a total area of 417 square miles (1,080 km), of which 417 square miles (1,080 km) is land and 0.6 square miles (1.6 km) (0.1%) is water.
As of the 2010 United States Census, there were 19,980 people, 7,720 households, and 5,377 families residing in the county. The population density was 48.0 inhabitants per square mile (18.5/km). There were 8,390 housing units at an average density of 20.1 per square mile (7.8/km). The racial makeup of the county was 95.7% white, 0.4% Asian, 0.3% black or African American, 0.2% American Indian, 2.3% from other races, and 1.2% from two or more races. Those of Hispanic or Latino origin made up 6.1% of the population. In terms of ancestry, 29.6% were German, 12.6% were American, 12.1% were English, and 10.7% were Irish.
Of the 7,720 households, 32.6% had children under the age of 18 living with them, 57.0% were married couples living together, 8.5% had a female householder with no husband present, 30.3% were non-families, and 26.1% of all households were made up of individuals. The average household size was 2.57 and the average family size was 3.11. The median age was 38.7 years.
The median income for a household in the county was $46,941 and the median income for a family was $60,352. Males had a median income of $41,318 versus $28,731 for females. The per capita income for the county was $21,438. About 7.1% of families and 10.2% of the population were below the poverty line, including 14.0% of those under age 18 and 7.2% of those age 65 or over.