Greene County is a county located in the U.S. state of Illinois. According to the 2010 United States Census, it has a population of 13,886. Its county seat is Carrollton.
According to the US Census Bureau, the county has a total area of 546 square miles (1,410 km), of which 543 square miles (1,410 km) is land and 3.3 square miles (8.5 km) (0.6%) is water.
As of the 2010 United States Census, there were 13,886 people, 5,570 households, and 3,777 families residing in the county. The population density was 25.6 inhabitants per square mile (9.9/km). There were 6,389 housing units at an average density of 11.8 per square mile (4.6/km). The racial makeup of the county was 97.9% white, 0.9% black or African American, 0.2% American Indian, 0.1% Asian, 0.3% from other races, and 0.7% from two or more races. Those of Hispanic or Latino origin made up 0.8% of the population. In terms of ancestry, 30.7% were German, 14.7% were Irish, 13.3% were English, and 12.1% were American.
Of the 5,570 households, 30.9% had children under the age of 18 living with them, 53.0% were married couples living together, 9.4% had a female householder with no husband present, 32.2% were non-families, and 27.8% of all households were made up of individuals. The average household size was 2.44 and the average family size was 2.95. The median age was 41.6 years.
The median income for a household in the county was $41,450 and the median income for a family was $52,049. Males had a median income of $38,185 versus $27,231 for females. The per capita income for the county was $22,107. About 11.8% of families and 15.1% of the population were below the poverty line, including 22.1% of those under age 18 and 10.0% of those age 65 or over.