List of Counties in Illinois
Illinois has 102 counties. The most populous counties are Cook County (Chicago), DuPage County, Lake County, Will County, Kane County, McHenry County, Winnebago County, Madison County, St. Clair County, and Sangamon County (Springfield). Cook County is the largest by far, with Chicago making it the second-most populous county in the U.S. Other populous counties surround Chicago and form part of its metropolitan area, contributing to Illinois’s economic and cultural significance. Outside the Chicago area, counties like Sangamon and Madison are important for government and industry.
List of All Counties in Illinois
- Adams County, Illinois
- Alexander County, Illinois
- Bond County, Illinois
- Boone County, Illinois
- Brown County, Illinois
- Bureau County, Illinois
- Calhoun County, Illinois
- Carroll County, Illinois
- Cass County, Illinois
- Champaign County, Illinois
- Christian County, Illinois
- Clark County, Illinois
- Clay County, Illinois
- Clinton County, Illinois
- Coles County, Illinois
- Cook County, Illinois
- Crawford County, Illinois
- Cumberland County, Illinois
- DeKalb County, Illinois
- DeWitt County, Illinois
- Douglas County, Illinois
- DuPage County, Illinois
- Edgar County, Illinois
- Edwards County, Illinois
- Effingham County, Illinois
- Fayette County, Illinois
- Ford County, Illinois
- Franklin County, Illinois
- Fulton County, Illinois
- Gallatin County, Illinois
- Greene County, Illinois
- Grundy County, Illinois
- Hamilton County, Illinois
- Hancock County, Illinois
- Hardin County, Illinois
- Henderson County, Illinois
- Henry County, Illinois
- Iroquois County, Illinois
- Jackson County, Illinois
- Jasper County, Illinois
- Jefferson County, Illinois
- Jersey County, Illinois
- Jo Daviess County, Illinois
- Johnson County, Illinois
- Kane County, Illinois
- Kankakee County, Illinois
- Kendall County, Illinois
- Knox County, Illinois
- Lake County, Illinois
- LaSalle County, Illinois
- Lawrence County, Illinois
- Lee County, Illinois
- Livingston County, Illinois
- Logan County, Illinois
- Macon County, Illinois
- Macoupin County, Illinois
- Madison County, Illinois
- Marion County, Illinois
- Marshall County, Illinois
- Mason County, Illinois
- Massac County, Illinois
- McDonough County, Illinois
- McHenry County, Illinois
- McLean County, Illinois
- Menard County, Illinois
- Mercer County, Illinois
- Monroe County, Illinois
- Montgomery County, Illinois
- Morgan County, Illinois
- Moultrie County, Illinois
- Ogle County, Illinois
- Peoria County, Illinois
- Perry County, Illinois
- Piatt County, Illinois
- Pike County, Illinois
- Pope County, Illinois
- Pulaski County, Illinois
- Putnam County, Illinois
- Randolph County, Illinois
- Richland County, Illinois
- Rock Island County, Illinois
- Saint Clair County, Illinois
- Saline County, Illinois
- Sangamon County, Illinois
- Schuyler County, Illinois
- Scott County, Illinois
- Shelby County, Illinois
- Stark County, Illinois
- Stephenson County, Illinois
- Tazewell County, Illinois
- Union County, Illinois
- Vermilion County, Illinois
- Wabash County, Illinois
- Warren County, Illinois
- Washington County, Illinois
- Wayne County, Illinois
- White County, Illinois
- Whiteside County, Illinois
- Will County, Illinois
- Williamson County, Illinois
- Winnebago County, Illinois
- Woodford County, Illinois
1. McLean County
Overview
McLean County is the largest county in Illinois by land area, located in the central part of the state. It is bordered by Logan County to the west, Livingston County to the northeast, and DeWitt County to the south. The county seat is Bloomington, which forms a twin-city area with Normal and serves as a hub for education, healthcare, and transportation. McLean County’s economy is diverse, with key sectors including agriculture, education, and insurance, as it is home to the headquarters of State Farm Insurance. The county also benefits from being located along major transportation routes, including interstates and railroads. Established in 1830, McLean County has a rich history tied to early settlers and agriculture, which remains a major part of the local economy.
County Facts
- Population: Approximately 170,000 (2023 estimate)
- County Seat: Bloomington
- Major Airports: Central Illinois Regional Airport (Bloomington-Normal)
- Major Highways: I-55, I-74, I-39, US-51, US-150
2. LaSalle County
Overview
LaSalle County is located in north-central Illinois, bordered by Kendall County to the northeast, Grundy County to the east, and Bureau County to the west. The county seat is Ottawa, a city known for its role in Illinois’ legal and political history. LaSalle County has a diverse economy based on agriculture, manufacturing, and tourism, with Starved Rock State Park being a major tourist destination. The Illinois River runs through the county, providing transportation and recreational opportunities. Established in 1831, LaSalle County played a significant role in the development of Illinois’ canal system, and its historical importance includes being a center of early industry and politics in the state.
County Facts
- Population: Approximately 108,000 (2023 estimate)
- County Seat: Ottawa
- Major Airports: Illinois Valley Regional Airport (Peru)
- Major Highways: I-80, I-39, US-6, US-34
3. Cook County
Overview
Cook County is located in northeastern Illinois and is the most populous county in the state, home to nearly 40% of the state’s population. It is bordered by Lake Michigan to the east, Lake County to the north, and Will County to the south. The county seat is Chicago, which is the third-largest city in the United States and serves as a major cultural, financial, and transportation hub. Cook County’s economy is driven by a wide range of industries, including finance, manufacturing, healthcare, and technology. The county is also home to major institutions like the Chicago Board of Trade, O’Hare International Airport, and several world-class universities and cultural institutions. Established in 1831, Cook County has a rich history, playing a pivotal role in the industrialization and development of the Midwest.
County Facts
- Population: Approximately 5.1 million (2023 estimate)
- County Seat: Chicago
- Major Airports: O’Hare International Airport, Midway International Airport
- Major Highways: I-90, I-94, I-55, I-290, I-294, US-41
4. Lake County
Overview
Lake County is located in northeastern Illinois, bordered by Lake Michigan to the east and Wisconsin to the north. The county seat is Waukegan, a city known for its industrial history and location along the lakefront. Lake County is part of the greater Chicago metropolitan area and is one of the wealthiest counties in the state. The county has a diverse economy that includes healthcare, finance, and manufacturing, and is home to several corporate headquarters, including Abbott Laboratories and Baxter International. Its location along Lake Michigan and access to natural resources like forest preserves make it a popular residential area for commuters working in Chicago. Established in 1839, Lake County has a long history tied to shipping and manufacturing.
County Facts
- Population: Approximately 720,000 (2023 estimate)
- County Seat: Waukegan
- Major Airports: Chicago Executive Airport
- Major Highways: I-94, I-294, US-41, IL-83
5. Will County
Overview
Will County is located in northeastern Illinois, south of Cook County, and is part of the greater Chicago metropolitan area. The county seat is Joliet, a historic city known for its industrial and transportation legacy, particularly its ties to the Illinois and Michigan Canal. Will County has seen significant population growth in recent decades, becoming a suburban hub with a mix of residential communities, manufacturing, and logistics industries. The county is also home to one of the nation’s largest intermodal facilities in Elwood, serving as a key distribution center for the Midwest. Will County was established in 1836 and has played an important role in the development of transportation and commerce in Illinois.
County Facts
- Population: Approximately 710,000 (2023 estimate)
- County Seat: Joliet
- Major Airports: Lewis University Airport
- Major Highways: I-55, I-80, I-355, US-30, US-52
6. Kankakee County
Overview
Kankakee County is located in northeastern Illinois, south of Will County. The county seat is Kankakee, a city situated along the Kankakee River that serves as a regional center for healthcare, education, and agriculture. The county has a strong agricultural base, with corn, soybeans, and dairy farming being key contributors to the local economy. In addition to agriculture, Kankakee County has growing industries in healthcare, education, and manufacturing. The county was established in 1853 and has a rich history of French settlement and Native American heritage, as well as being part of the early agricultural development of the state.
County Facts
- Population: Approximately 105,000 (2023 estimate)
- County Seat: Kankakee
- Major Airports: Greater Kankakee Airport
- Major Highways: I-57, US-45, US-52, IL-17
7. DeKalb County
Overview
DeKalb County is located in northern Illinois, west of Kane County and south of Boone County. The county seat is Sycamore, while DeKalb, home to Northern Illinois University, is the county’s largest city. DeKalb County is known for its agricultural production, particularly corn and soybeans, and the presence of NIU makes education a major part of the local economy. DeKalb also has a rich history of innovation, being the birthplace of barbed wire manufacturing in the 19th century. Established in 1837, DeKalb County has maintained a blend of rural and suburban communities, with modern industries complementing its strong agricultural roots.
County Facts
- Population: Approximately 105,000 (2023 estimate)
- County Seat: Sycamore
- Major Airports: DeKalb Taylor Municipal Airport
- Major Highways: I-88, US-38, IL-23, IL-64
8. Sangamon County
Overview
Sangamon County is located in central Illinois, with Springfield serving as both the county seat and the state capital. The county is bordered by Logan County to the north and Macon County to the east. Sangamon County is a political and economic hub for the state, with government services, healthcare, and education being major sectors of its economy. Springfield is home to many historic sites related to Abraham Lincoln, including the Abraham Lincoln Presidential Library and Museum, making tourism an important part of the local economy. Established in 1821, Sangamon County has played a critical role in Illinois’ political history and development.
County Facts
- Population: Approximately 195,000 (2023 estimate)
- County Seat: Springfield
- Major Airports: Abraham Lincoln Capital Airport
- Major Highways: I-55, I-72, US-36, US-66, IL-97
9. Peoria County
Overview
Peoria County is located in central Illinois, along the Illinois River, and is home to the city of Peoria, the county seat and one of the oldest European settlements in the state. Peoria has long been an industrial center, particularly known for being the headquarters of Caterpillar Inc., a global leader in construction and mining equipment. The county’s economy is driven by manufacturing, healthcare, and agriculture, with the Illinois River serving as a vital transportation route for goods. Established in 1825, Peoria County played an important role in the industrialization of Illinois and continues to be a significant economic hub in the state.
County Facts
- Population: Approximately 180,000 (2023 estimate)
- County Seat: Peoria
- Major Airports: General Wayne A. Downing Peoria International Airport
- Major Highways: I-74, I-474, US-24, IL-6
10. Champaign County
Overview
Champaign County is located in east-central Illinois, bordered by Vermilion County to the east and Piatt County to the west. The county seat is Urbana, which, along with neighboring Champaign, forms a twin-city area. Champaign County is home to the University of Illinois at Urbana-Champaign, one of the top public research universities in the country, making education, research, and technology major drivers of the local economy. The county also has a strong agricultural sector, producing corn and soybeans. Established in 1833, Champaign County has evolved into a center for higher education and innovation, while maintaining its agricultural heritage.
County Facts
- Population: Approximately 210,000 (2023 estimate)
- County Seat: Urbana
- Major Airports: University of Illinois Willard Airport
- Major Highways: I-57, I-74, US-45, US-150