Will County is a county in the northeastern part of the state of Illinois. According to the 2020 census, it had a population of 696,355, an increase of 2.8% from 677,560 in 2010, making it Illinois's fourth-most populous county.^[1] The county seat is Joliet.^[2] Will County is one of the five collar counties of the Chicago–Naperville–Elgin, IL–IN–WI Metropolitan Statistical Area. The portion of Will County around Joliet uses area codes 815 and 779, while 630 and 331 are for far northern Will County and 708 is for central and eastern Will County.

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Will County
County
Flanders House in Plainfield (1840), Midewin National Tallgrass Prairie.
Location within the U.S. state of Illinois
Illinois's location within the U.S.
Coordinates: 41°26′42″N 87°58′43″W
Country	United States
State	Illinois
Founded	January 12, 1836
Named for	Conrad Will
Seat	Joliet
Largest city	Joliet
Area
• Total	849 sq mi (2,200 km2)
• Land	837 sq mi (2,170 km2)
• Water	12 sq mi (30 km2)  1.5%
Population  (2020)
• Total	696,355
• Density	820/sq mi (320/km2)
Time zone	UTC−6 (Central)
• Summer (DST)	UTC−5 (CDT)
Congressional districts	1st, 2nd, 11th, 14th
Website	www.willcountyillinois.com

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Will County was formed on January 12, 1836, out of Cook and Iroquois Counties. It was named after Conrad Will, a politician and businessman involved in salt production in southern Illinois.^[3] Will was a member of the first Illinois Constitutional Convention and a member of the Illinois legislature until his death in 1835. Besides its present area, the county originally included the part of Kankakee County, Illinois, north of the Kankakee River. It lost that area when Kankakee County was organized in 1852. Since then its boundaries have not changed.

36 locations in Will County are on the National Register of Historic Places.

• Will County from its 1836 creation to 1852
• Will County in 1853, reduced to its current borders by the creation of Kankakee County

According to the U.S. Census Bureau, the county has an area of 849 square miles (2,200 km²), of which 837 square miles (2,170 km²) is land and 12 square miles (31 km²) (1.5%) is water.^[4]

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 km²) total) under the Forest Preserve District of Will County. The 17,000 acres (69 km²) 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.^[12] The population density was 809.6 inhabitants per square mile (312.6/km²). There were 237,501 housing units at an average density of 283.8 per square mile (109.6/km²).^[4] 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.^[12] 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.^[13]

Of the 225,256 households, 44.0% had children under 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.^[12]

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 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 18 and 5.6% of those 65 or older.^[14]

Will County is governed by a 22-member county board elected from 11 districts. Each district elects two members. The county executive, county clerk, coroner, auditor, treasurer, recorder of deeds, state's attorney, and sheriff are all elected in a countywide vote.

Will County government has been housed in a succession of courthouses, the first being erected in 1837.^[15] The fourth courthouse was designed of reinforced concrete in the Brutalist style by Otto Stark of C.F. Murphy Associates and completed in 1969. Citing lack of space, inefficiency and high operating costs, the County Board chose to erect a new courthouse, which was designed by Wight & Co. and completed in 2020.^[16] Considerable controversy surrounded the disposition of the 1969 courthouse, with Landmarks Preservation Council of Illinois including the building on its “2022 Most Endangered Historic Places in Illinois”.^[17] After a number of votes and appeals, demolition was approved and the destruction of the building began on 4 December 2023.^[18]

Like most of the collar counties, Will County was once a Republican stronghold. It went Republican in all but three elections from 1892 to 1988. Since the 1990s, it has become a swing county. It voted for the national winner in every presidential election from 1980 to 2012, but Chicago-born Hillary Clinton won it along with the rest of the "collar counties" aside from McHenry in 2016.

• Governors State University is a 6,000-student public university in University Park.
• Lewis University is a 5,200-student four-year private university in Romeoville.
• University of St. Francis is a 3,300-student four-year private university in Joliet.
• The county is in Community College District 525 and is served by Joliet Junior College in Joliet.^[20] Joliet Junior College was the first two-year higher education institution in the United States.

Will County is served by four U.S. interstate highways, four U.S. highways, and 12 Illinois highways. Pace provides bus transit services within the county.

The municipalities with their population within Will County and their total population as of the 2010 census are:^[23]