Stephenson County is a county located in the U.S. state of Illinois. According to the 2010 United States Census, it had a population of 47,711. Its county seat is Freeport.
According to the US Census Bureau, the county has a total area of 565 square miles (1,460 km), of which 565 square miles (1,460 km) is land and 0.5 square miles (1.3 km) (0.09%) is water.
As of the 2010 United States Census, there were 47,711 people, 19,845 households, and 13,015 families residing in the county. The population density was 84.5 inhabitants per square mile (32.6/km). There were 22,081 housing units at an average density of 39.1 per square mile (15.1/km). The racial makeup of the county was 86.5% white, 9.0% black or African American, 0.6% Asian, 0.2% American Indian, 1.2% from other races, and 2.5% from two or more races. Those of Hispanic or Latino origin made up 2.9% of the population. In terms of ancestry, 46.6% were German, 12.5% were Irish, 10.0% were English, and 8.0% were American.
Of the 19,845 households, 28.6% had children under the age of 18 living with them, 50.3% were married couples living together, 11.2% had a female householder with no husband present, 34.4% were non-families, and 29.7% of all households were made up of individuals. The average household size was 2.36 and the average family size was 2.90. The median age was 43.1 years.
The median income for a household in the county was $43,304 and the median income for a family was $54,224. Males had a median income of $41,672 versus $29,510 for females. The per capita income for the county was $22,608. About 12.3% of families and 14.8% of the population were below the poverty line, including 24.1% of those under age 18 and 7.3% of those age 65 or over.