Henderson County is a county located in the U.S. state of Illinois. According to the 2010 United States Census, it has a population of 7,331. Its county seat is Oquawka.
According to the US Census Bureau, the county has a total area of 395 square miles (1,020 km), of which 379 square miles (980 km) is land and 16 square miles (41 km) (4.1%) is water.
As of the 2010 United States Census, there were 7,331 people, 3,149 households, and 2,127 families residing in the county. The population density was 19.3 inhabitants per square mile (7.5/km). There were 3,827 housing units at an average density of 10.1 per square mile (3.9/km). The racial makeup of the county was 98.2% white, 0.2% Asian, 0.2% American Indian, 0.2% black or African American, 0.1% Pacific islander, 0.2% from other races, and 1.0% from two or more races. Those of Hispanic or Latino origin made up 1.1% of the population. In terms of ancestry, 24.4% were German, 14.5% were Irish, 11.9% were English, 5.9% were Swedish, and 5.0% were American.
Of the 3,149 households, 26.9% had children under the age of 18 living with them, 54.9% were married couples living together, 8.7% had a female householder with no husband present, 32.5% were non-families, and 27.3% of all households were made up of individuals. The average household size was 2.31 and the average family size was 2.78. The median age was 47.2 years.
The median income for a household in the county was $43,450 and the median income for a family was $55,154. Males had a median income of $41,052 versus $27,426 for females. The per capita income for the county was $22,492. About 7.8% of families and 11.4% of the population were below the poverty line, including 13.3% of those under age 18 and 8.3% of those age 65 or over.