Illinois Counties List
There are a total of 102 counties in the state of Illinois. Among them, St. Clair County is the oldest one (established in 1790) while Douglas County is the youngest (established in 1859). With population of 5,194,675, Cook County is the most populated. The biggest county by land area is McLean County (3,067 km²) and the smallest is Putnam County (414 km²).
Largest Counties in Illinois
1. McLean County
County Seat: Bloomington
- Area: 1,186 square miles
- Population: Approximately 170,954 (2020 census)
- Area Codes: 309
- Latitude: 40.4842° N
- Longitude: 88.9937° W
Location and History
McLean County is the largest county by area in Illinois, located in the central part of the state. Established in 1830, the county was named after John McLean, a U.S. Senator from Illinois. Bloomington, the county seat, is one of the twin cities (along with Normal) that serve as the economic and cultural hub of the region. The county’s history is deeply connected to agriculture, particularly corn and soybean production, and later became a center for transportation and education with the establishment of Illinois Wesleyan University and Illinois State University in nearby Normal. McLean County’s growth was significantly influenced by the arrival of the railroad in the mid-19th century, making Bloomington a key stop on the Chicago & Alton Railroad.
Major Highways and Landmarks
McLean County is intersected by major highways, including Interstate 55, which runs north-south through the county, connecting it to Chicago and St. Louis. Interstate 74 and Interstate 39 also pass through the county, providing access to Peoria, Champaign, and Rockford. Significant landmarks include the David Davis Mansion, home of Abraham Lincoln’s close friend and Supreme Court Justice David Davis, and the McLean County Museum of History, located in the historic courthouse in downtown Bloomington. The county is also known for the Constitution Trail, a popular walking and biking path that runs through Bloomington-Normal, and the Ewing Manor and Cultural Center, which hosts numerous cultural and artistic events.
2. LaSalle County
County Seat: Ottawa
- Area: 1,148 square miles
- Population: Approximately 109,658 (2020 census)
- Area Codes: 815, 779
- Latitude: 41.3333° N
- Longitude: 88.8330° W
Location and History
LaSalle County is located in north-central Illinois and was established in 1831. The county was named after the French explorer René-Robert Cavelier, Sieur de La Salle, who explored the region in the 17th century. Ottawa, the county seat, played a significant role in the early political history of Illinois, notably as the site of the first Lincoln-Douglas debate in 1858. The county’s economy has historically been based on agriculture and mining, particularly coal, though manufacturing and tourism have become increasingly important. LaSalle County is also known for its scenic beauty, with the Illinois River running through the county and several state parks attracting visitors.
Major Highways and Landmarks
LaSalle County is served by major highways such as Interstate 80, which runs east-west across the northern part of the county, and Interstate 39, which runs north-south. U.S. Route 6 and U.S. Route 52 are also key routes in the region. Key landmarks include Starved Rock State Park, one of Illinois’ most popular natural attractions, known for its canyons, waterfalls, and hiking trails. The county is also home to Matthiessen State Park, another scenic area with rock formations and waterfalls, and the Hegeler Carus Mansion in LaSalle, a National Historic Landmark that reflects the county’s industrial heritage. The Illinois & Michigan Canal National Heritage Corridor, which runs through Ottawa, celebrates the history of the canal that connected the Great Lakes to the Mississippi River.
3. Kankakee County
County Seat: Kankakee
- Area: 681 square miles
- Population: Approximately 107,502 (2020 census)
- Area Codes: 815, 779
- Latitude: 41.1200° N
- Longitude: 87.8616° W
Location and History
Kankakee County is located in northeastern Illinois, just south of the Chicago metropolitan area. The county was established in 1853 and named after the Kankakee River, which flows through the region. Kankakee, the county seat, developed as a key agricultural and transportation hub in the 19th century, particularly after the arrival of the Illinois Central Railroad. The county has a diverse economy, with agriculture, manufacturing, and services playing significant roles. Kankakee County is also known for its natural beauty, with the Kankakee River providing opportunities for recreation and conservation.
Major Highways and Landmarks
Kankakee County is accessible via Interstate 57, which runs north-south through the county, connecting it to Chicago to the north and Champaign to the south. U.S. Route 45/52 and Illinois Route 17 are also important highways in the region. Notable landmarks include the Kankakee River State Park, which offers hiking, fishing, camping, and canoeing along the scenic Kankakee River. The Frank Lloyd Wright-designed B. Harley Bradley House, located in Kankakee, is a significant example of the Prairie School architectural style and is open for tours. The county also hosts the annual Kankakee River Valley Fishing Derby, which attracts anglers from across the state.
4. Iroquois County
County Seat: Watseka
- Area: 1,117 square miles
- Population: Approximately 27,077 (2020 census)
- Area Codes: 815, 779
- Latitude: 40.7785° N
- Longitude: 87.7320° W
Location and History
Iroquois County is located in east-central Illinois, along the Indiana border. Established in 1833, the county was named after the Iroquois Confederacy, although the Iroquois people did not historically inhabit the area. Watseka, the county seat, is named after a Native American woman of the Potawatomi tribe, reflecting the region’s indigenous heritage. The county’s economy has long been based on agriculture, with corn, soybeans, and dairy farming being the primary industries. Iroquois County is known for its rural landscapes and small-town charm, with many historic sites and buildings preserved throughout the county.
Major Highways and Landmarks
Iroquois County is served by U.S. Route 24, which runs east-west through the county, and U.S. Route 52, which runs north-south. Interstate 57 also passes through the western part of the county, providing access to Chicago and southern Illinois. Significant landmarks include the Old Courthouse Museum in Watseka, which houses exhibits on the county’s history and culture, and the Iroquois County State Wildlife Area, a popular destination for hunting, fishing, and birdwatching. The county is also home to several historic churches and cemeteries that reflect the area’s 19th-century settlement patterns. The annual Watseka Park Festival is a key cultural event in the county, celebrating local heritage with parades, music, and community activities.
5. Livingston County
County Seat: Pontiac
- Area: 1,044 square miles
- Population: Approximately 35,815 (2020 census)
- Area Codes: 815, 779
- Latitude: 40.8806° N
- Longitude: 88.6295° W
Location and History
Livingston County is located in central Illinois and was established in 1837. The county was named after Edward Livingston, a prominent U.S. statesman and jurist. Pontiac, the county seat, developed as a major stop along the historic Route 66, which contributed to the county’s growth and development in the 20th century. Livingston County’s economy has traditionally been based on agriculture, with corn and soybeans being the dominant crops, though manufacturing and services have become more significant in recent decades. The county is known for its historic sites, scenic landscapes, and strong connection to Route 66.
Major Highways and Landmarks
Livingston County is intersected by Interstate 55, which runs north-south through the county, following the path of historic Route 66. U.S. Route 24 and Illinois Route 116 are also important highways in the region. Key landmarks include the Pontiac-Oakland Automobile Museum, which celebrates the history of the Pontiac car brand and Route 66. The Livingston County Courthouse, located in downtown Pontiac, is a historic building that serves as the center of county government. The county is also home to the Route 66 Hall of Fame & Museum, which features exhibits on the history of the “Mother Road” and its impact on American culture. The Vermilion River, which runs through the county, offers opportunities for fishing, canoeing, and nature observation.
6. DeKalb County
County Seat: Sycamore
- Area: 634 square miles
- Population: Approximately 100,420 (2020 census)
- Area Codes: 815, 779
- Latitude: 41.8885° N
- Longitude: 88.7642° W
Location and History
DeKalb County is located in northern Illinois, west of Chicago. Established in 1837, the county was named after Johann de Kalb, a German-born hero of the American Revolutionary War. Sycamore, the county seat, has a rich history and is known for its well-preserved historic downtown. The city of DeKalb, home to Northern Illinois University (NIU), is the largest city in the county and serves as a major educational and cultural center. The county’s economy is diverse, with agriculture, education, manufacturing, and healthcare playing significant roles. DeKalb County is also known for its contributions to agricultural innovation, particularly in the development of hybrid corn.
Major Highways and Landmarks
DeKalb County is served by Interstate 88, which runs east-west through the southern part of the county, and U.S. Route 30, which also runs east-west. Illinois Route 23 is a key north-south route. Notable landmarks include the Ellwood House Museum in DeKalb, a historic mansion that reflects the county’s agricultural heritage, and the DeKalb County Courthouse in Sycamore, a beautiful example of Beaux-Arts architecture. The NIU campus in DeKalb is a major cultural hub, hosting numerous events, performances, and exhibitions. The county is also home to the Sycamore Pumpkin Festival, an annual event that draws visitors from across the region to celebrate the harvest season with parades, contests, and family activities.
7. Will County
County Seat: Joliet
- Area: 837 square miles
- Population: Approximately 696,355 (2020 census)
- Area Codes: 815, 779
- Latitude: 41.5055° N
- Longitude: 88.0817° W
Location and History
Will County is located in northeastern Illinois, just south of Chicago. Established in 1836, the county was named after Conrad Will, a politician and businessman who played a key role in the early development of Illinois. Joliet, the county seat, is one of the largest cities in the state and has a rich history as an industrial and transportation hub. The county’s economy has traditionally been based on manufacturing, transportation, and agriculture, though it has diversified in recent years to include services, logistics, and healthcare. Will County is part of the Chicago metropolitan area and has experienced significant growth and suburbanization in the past few decades.
Major Highways and Landmarks
Will County is intersected by several major highways, including Interstate 55, which runs north-south, and Interstate 80, which runs east-west through the county. Interstate 355, the Veterans Memorial Tollway, also runs through the county, providing access to the western suburbs of Chicago. Significant landmarks include the Joliet Iron Works Historic Site, which preserves the remains of one of the largest steel mills in the country, and the Rialto Square Theatre in downtown Joliet, a historic vaudeville theater that is still in use today. The county is also home to the Midewin National Tallgrass Prairie, a large conservation area dedicated to restoring native prairie ecosystems. The Illinois & Michigan Canal National Heritage Corridor, which runs through the county, celebrates the history of the canal that connected the Great Lakes to the Mississippi River.
8. Champaign County
County Seat: Urbana
- Area: 998 square miles
- Population: Approximately 205,865 (2020 census)
- Area Codes: 217
- Latitude: 40.1138° N
- Longitude: 88.1970° W
Location and History
Champaign County is located in east-central Illinois and was established in 1833. The county was named after Champaign County, Ohio, from which many early settlers came. Urbana, the county seat, is part of the Champaign-Urbana metropolitan area, which is also home to the University of Illinois at Urbana-Champaign (UIUC). The university, one of the top public research institutions in the country, is the largest employer in the county and plays a central role in its economy, culture, and identity. The county’s economy is also supported by agriculture, with corn and soybeans being the primary crops.
Major Highways and Landmarks
Champaign County is served by Interstate 74, which runs east-west through the county, and Interstate 57, which runs north-south. U.S. Route 45 and U.S. Route 150 are also important highways in the region. Notable landmarks include the Krannert Art Museum and the Spurlock Museum, both located on the UIUC campus, which offer extensive collections of art, history, and culture. The county is also home to the Urbana Sweetcorn Festival, an annual event that celebrates the agricultural heritage of the region. The Champaign County Courthouse in Urbana is another significant landmark, reflecting the county’s rich history and architectural heritage. The county’s robust research and technology sectors have earned it a reputation as a hub of innovation in Illinois.
9. Peoria County
County Seat: Peoria
- Area: 629 square miles
- Population: Approximately 181,830 (2020 census)
- Area Codes: 309
- Latitude: 40.6936° N
- Longitude: 89.5889° W
Location and History
Peoria County is located in central Illinois, along the Illinois River. Established in 1825, the county was named after the Peoria, a Native American tribe that historically inhabited the region. Peoria, the county seat, is one of the oldest European settlements in Illinois and developed as a major manufacturing and transportation hub in the 19th and 20th centuries. The county’s economy has traditionally been based on manufacturing, particularly heavy equipment, with Caterpillar Inc., one of the world’s largest construction and mining equipment manufacturers, headquartered in Peoria. In recent years, the economy has diversified to include healthcare, education, and services.
Major Highways and Landmarks
Peoria County is served by Interstate 74, which runs east-west through Peoria, and Interstate 474, which provides a bypass around the city. U.S. Route 24 and U.S. Route 150 also run through the county. Key landmarks include the Peoria Riverfront, a vibrant area with parks, museums, and cultural attractions, including the Peoria Riverfront Museum and the Caterpillar Visitors Center. The county is also home to the Peoria Zoo and Luthy Botanical Garden, both located in Glen Oak Park. The Peoria Civic Center, a major venue for concerts, sports, and conventions, is another significant landmark. The county’s history is preserved at sites like the Pettengill-Morron House, a historic mansion that offers tours and educational programs.
10. Kane County
County Seat: Geneva
- Area: 524 square miles
- Population: Approximately 532,403 (2020 census)
- Area Codes: 630, 331
- Latitude: 41.8889° N
- Longitude: 88.4016° W
Location and History
Kane County is located in northeastern Illinois, just west of Chicago. Established in 1836, the county was named after Elias Kane, an Illinois senator. Geneva, the county seat, is known for its historic downtown and riverfront, while the city of Aurora, the second-largest city in Illinois, is a major cultural and economic center in the county. Kane County has experienced significant growth in recent decades as part of the Chicago metropolitan area, with a diverse economy that includes manufacturing, retail, healthcare, and services. The county is known for its rich history, scenic Fox River, and strong sense of community.
Major Highways and Landmarks
Kane County is intersected by several major highways, including Interstate 88, which runs east-west through the southern part of the county, and U.S. Route 20, which runs east-west through the northern part. Illinois Route 31 and Illinois Route 25 run parallel to the Fox River, providing access to the county’s riverfront communities. Significant landmarks include the Fabyan Villa Museum and Japanese Garden in Geneva, which offers insights into the life of Colonel George Fabyan and features beautifully landscaped gardens. The Fox River Trail, a popular biking and walking path, runs through the county, offering scenic views and access to several parks and nature preserves. The county is also home to the historic Paramount Theatre in Aurora, a major venue for live performances and cultural events.
List of All Counties in Illinois
Below please see all Illinois counties which are listed in alphabetical order.
- Adams County, IL
- Alexander County, IL
- Bond County, IL
- Boone County, IL
- Brown County, IL
- Bureau County, IL
- Calhoun County, IL
- Carroll County, IL
- Cass County, IL
- Champaign County, IL
- Christian County, IL
- Clark County, IL
- Clay County, IL
- Clinton County, IL
- Coles County, IL
- Cook County, IL
- Crawford County, IL
- Cumberland County, IL
- DeKalb County, IL
- DeWitt County, IL
- Douglas County, IL
- DuPage County, IL
- Edgar County, IL
- Edwards County, IL
- Effingham County, IL
- Fayette County, IL
- Ford County, IL
- Franklin County, IL
- Fulton County, IL
- Gallatin County, IL
- Greene County, IL
- Grundy County, IL
- Hamilton County, IL
- Hancock County, IL
- Hardin County, IL
- Henderson County, IL
- Henry County, IL
- Iroquois County, IL
- Jackson County, IL
- Jasper County, IL
- Jefferson County, IL
- Jersey County, IL
- Jo Daviess County, IL
- Johnson County, IL
- Kane County, IL
- Kankakee County, IL
- Kendall County, IL
- Knox County, IL
- Lake County, IL
- LaSalle County, IL
- Lawrence County, IL
- Lee County, IL
- Livingston County, IL
- Logan County, IL
- Macon County, IL
- Macoupin County, IL
- Madison County, IL
- Marion County, IL
- Marshall County, IL
- Mason County, IL
- Massac County, IL
- McDonough County, IL
- McHenry County, IL
- McLean County, IL
- Menard County, IL
- Mercer County, IL
- Monroe County, IL
- Montgomery County, IL
- Morgan County, IL
- Moultrie County, IL
- Ogle County, IL
- Peoria County, IL
- Perry County, IL
- Piatt County, IL
- Pike County, IL
- Pope County, IL
- Pulaski County, IL
- Putnam County, IL
- Randolph County, IL
- Richland County, IL
- Rock Island County, IL
- Saint Clair County, IL
- Saline County, IL
- Sangamon County, IL
- Schuyler County, IL
- Scott County, IL
- Shelby County, IL
- Stark County, IL
- Stephenson County, IL
- Tazewell County, IL
- Union County, IL
- Vermilion County, IL
- Wabash County, IL
- Warren County, IL
- Washington County, IL
- Wayne County, IL
- White County, IL
- Whiteside County, IL
- Will County, IL
- Williamson County, IL
- Winnebago County, IL
- Woodford County, IL
Map of Illinois Counties
