Will County is a county in the northeastern part of the state of Illinois. According to the 2010 census, it had a population of 677,560, which is an increase of 34.9% from 502,266 in 2000, making it the fourth-most populous county in Illinois. The county seat is Joliet.
According to the U.S. Census Bureau, the county has an area of 849 square miles (2,200 km), of which 837 square miles (2,170 km) is land and 12 square miles (31 km) (1.5%) is water.
The Kankakee River, Du Page River and the Des Plaines River run through the county and join on its western border. The Illinois and Michigan Canal and the Chicago Sanitary and Ship Canal run through Will County.
A number of areas are preserved as parks (over 20,000 acres (81 km) total) under the Forest Preserve District of Will County. The 17,000 acres (69 km) Midewin National Tallgrass Prairie is a U.S. Forest Service park in the county on the grounds of the former Joliet Arsenal. Other parks include Channahon State Park and the Des Plaines Fish and Wildlife Area.
As of the 2010 Census, there were 677,560 people, 225,256 households, and 174,062 families residing in the county. The population density was 809.6 inhabitants per square mile (312.6/km). There were 237,501 housing units at an average density of 283.8 per square mile (109.6/km). The racial makeup of the county was 76.0% white, 11.2% black or African American, 4.6% Asian, 0.3% American Indian, 5.8% from other races, and 2.3% from two or more races. Those of Hispanic or Latino origin made up 15.6% of the population. In terms of ancestry, 21.6% were German, 18.6% were Irish, 13.3% were Polish, 11.1% were Italian, 5.9% were English, and 2.1% were American.
Of the 225,256 households, 44.0% had children under the age of 18 living with them, 61.9% were married couples living together, 10.9% had a female householder with no husband present, 22.7% were non-families, and 18.5% of all households were made up of individuals. The average household size was 2.97 and the average family size was 3.41. The median age was 35.4 years.
The median income for a household in the county was $75,906 and the median income for a family was $85,488. Males had a median income of $60,867 versus $40,643 for females. The per capita income for the county was $29,811. About 5.0% of families and 6.6% of the population were below the poverty line, including 9.0% of those under age 18 and 5.6% of those age 65 or over.