Shelby County is a county located in the U.S. state of Illinois. According to the 2010 census, it had a population of 22,363. Its county seat is Shelbyville.
According to the U.S. Census Bureau, the county has a total area of 768 square miles (1,990 km), of which 759 square miles (1,970 km) is land and 9.5 square miles (25 km) (1.2%) is water.
As of the 2010 United States Census, there were 22,363 people, 9,216 households, and 6,376 families residing in the county. The population density was 29.5 inhabitants per square mile (11.4/km). There were 10,396 housing units at an average density of 13.7 per square mile (5.3/km). The racial makeup of the county was 98.6% white, 0.3% Asian, 0.2% American Indian, 0.2% black or African American, 0.2% from other races, and 0.6% from two or more races. Those of Hispanic or Latino origin made up 0.8% of the population. In terms of ancestry, 25.5% were German, 9.9% were English, 9.8% were American, and 8.8% were Irish.
Of the 9,216 households, 29.2% had children under the age of 18 living with them, 57.1% were married couples living together, 8.0% had a female householder with no husband present, 30.8% were non-families, and 27.1% of all households were made up of individuals. The average household size was 2.40 and the average family size was 2.90. The median age was 43.5 years.
The median income for a household in the county was $44,627 and the median income for a family was $55,655. Males had a median income of $40,119 versus $27,860 for females. The per capita income for the county was $21,891. About 7.8% of families and 11.3% of the population were below the poverty line, including 16.7% of those under age 18 and 8.1% of those age 65 or over.