Established as a state in 1818, Illinois became an industrial powerhouse, with Chicago playing a crucial role in transportation and commerce. It has 102 counties.
10 Largest Counties in Illinois
1. Cook County
County Facts:
- Population: Approximately 5.2 million
- Area Codes: 312, 773, 708, 847
- Zip Codes: 60001–60827
- County Seat: Chicago
Geography and History:
Cook County is located in northeastern Illinois, covering 1,635 square miles, and is bordered by Lake Michigan to the east. It is the most populous county in Illinois and the second most populous in the U.S. after Los Angeles County. The geography includes urban landscapes in Chicago and its suburbs, with some forest preserves and natural areas.
Cook County was established in 1831, named after Daniel Pope Cook, an early Illinois statesman. Chicago, the county seat, became a major transportation and economic hub in the 19th century due to its strategic location by Lake Michigan and the Chicago River. The Great Chicago Fire of 1871 led to a period of rapid rebuilding and growth. Over the decades, Cook County became a center for manufacturing, trade, and finance, with a diverse population from around the world.
Colleges and Universities:
- University of Illinois Chicago (UIC): A major public research university offering programs in medicine, engineering, business, and more.
- Northwestern University: A private research university in Evanston, known for its law, journalism, and business schools.
- DePaul University: A private university in Chicago, offering a range of undergraduate and graduate programs.
- Loyola University Chicago: A private Jesuit university with strong programs in law, business, and health sciences.
Major Landmarks:
Cook County is home to some of the most famous landmarks in the U.S., including the Willis Tower (formerly Sears Tower), Millennium Park, and the Art Institute of Chicago. Navy Pier, Lincoln Park Zoo, and the Magnificent Mile attract millions of tourists annually. The historic Wrigley Field, home to the Chicago Cubs, and Soldier Field, home to the Chicago Bears, are iconic sports venues. Additionally, the county’s extensive Forest Preserves offer natural green spaces for recreation.
2. DuPage County
County Facts:
- Population: Approximately 930,000
- Area Codes: 630, 331
- Zip Codes: 60101–60599
- County Seat: Wheaton
Geography and History:
DuPage County is located just west of Chicago, covering 336 square miles. The geography of the county includes suburban developments, forest preserves, and several rivers, including the DuPage River. The climate is typical of the Midwest, with cold winters and hot, humid summers.
The county was established in 1839 and named after the DuPage River, which was named for a French fur trapper. DuPage grew from a rural area to a suburban hub in the 20th century as Chicago expanded. Today, it is one of the wealthiest counties in Illinois and is known for its high standard of living, excellent schools, and corporate headquarters, including Navistar and McDonald’s (before it relocated).
Colleges and Universities:
- College of DuPage: One of the largest community colleges in the U.S., offering associate degrees and certifications in various fields.
- Elmhurst University: A private liberal arts college in Elmhurst, offering programs in nursing, business, and the arts.
- Benedictine University: A private Catholic university in Lisle, known for its strong programs in health sciences and business.
- Northern Illinois University (Naperville Campus): A regional campus offering graduate programs and continuing education.
Major Landmarks:
The Morton Arboretum, a world-renowned tree and plant research facility, is a key landmark in DuPage County. Cantigny Park in Wheaton features beautiful gardens, a museum dedicated to military history, and the historic McCormick House. The DuPage County Historical Museum preserves local history, and the county’s forest preserves, including Blackwell and Waterfall Glen, offer outdoor recreation.
3. Lake County
County Facts:
- Population: Approximately 714,000
- Area Codes: 847, 224
- Zip Codes: 60002–60099
- County Seat: Waukegan
Geography and History:
Lake County is located in northeastern Illinois, along the shores of Lake Michigan. The county covers 1,368 square miles and features a mix of suburban areas, lakes, rivers, and forest preserves. The Chain O’Lakes region in the western part of the county is a popular area for boating and fishing.
Lake County was established in 1839, with Waukegan serving as its county seat. Historically, the county grew as a transportation hub due to its proximity to Chicago and access to Lake Michigan. During the 20th century, suburban development expanded rapidly, making Lake County one of the most affluent and desirable places to live in Illinois.
Colleges and Universities:
- College of Lake County: A public community college offering associate degrees, certificates, and continuing education programs.
- Lake Forest College: A private liberal arts college known for its strong undergraduate programs in the humanities and sciences.
- Rosalind Franklin University of Medicine and Science: A graduate university focusing on health sciences, including medical, pharmacy, and biomedical programs.
- DeVry University (Gurnee Campus): Offers career-oriented programs in technology, business, and healthcare.
Major Landmarks:
One of the county’s most famous landmarks is the Illinois Beach State Park, located along the shores of Lake Michigan. The Ravinia Festival in Highland Park is the oldest outdoor music festival in the U.S., hosting world-class performances every summer. Six Flags Great America, a major amusement park in Gurnee, attracts millions of visitors. Other important sites include the historic Genesee Theatre in Waukegan and the Volo Auto Museum, which houses an impressive collection of vintage cars and Hollywood memorabilia.
4. Will County
County Facts:
- Population: Approximately 700,000
- Area Codes: 815, 779
- Zip Codes: 60401–60999
- County Seat: Joliet
Geography and History:
Will County, located in northeastern Illinois, spans 837 square miles and features a combination of urban, suburban, and rural areas. The Des Plaines and Kankakee Rivers run through the county, providing scenic waterways. The climate is typical of the Midwest, with four distinct seasons.
Established in 1836, Will County is named after Dr. Conrad Will, a pioneer and politician. Joliet, the county seat, grew as a manufacturing and transportation hub in the 19th and early 20th centuries, with industries such as steel production driving the local economy. In recent decades, Will County has become a major suburban area, with significant population growth due to its proximity to Chicago.
Colleges and Universities:
- Joliet Junior College: The first public community college in the U.S., offering a wide range of associate degrees, certifications, and workforce training.
- Lewis University: A private Catholic university in Romeoville, known for its programs in aviation, nursing, and criminal justice.
- University of St. Francis: A private Catholic university in Joliet offering undergraduate and graduate programs in business, healthcare, and education.
- Governors State University: A public university located in University Park, offering undergraduate and graduate degrees in a wide range of disciplines.
Major Landmarks:
The Joliet Area Historical Museum celebrates the rich history of the county, including its ties to Route 66. Chicagoland Speedway hosts NASCAR events, while the Rialto Square Theatre in Joliet is a historic venue for concerts and performances. The Midewin National Tallgrass Prairie, once the site of the Joliet Army Ammunition Plant, offers hiking and wildlife viewing. The Des Plaines River provides outdoor recreation opportunities, including boating and fishing.
5. Kane County
County Facts:
- Population: Approximately 534,000
- Area Codes: 630, 331, 847
- Zip Codes: 60110–60554
- County Seat: Geneva
Geography and History:
Kane County is located west of Chicago, covering 524 square miles. The Fox River runs through the heart of the county, with cities like Aurora and Elgin located along its banks. The geography of Kane County includes suburban areas, farmland, and forest preserves, with a typical Midwestern climate.
Kane County was founded in 1836 and named after Elias Kane, a prominent politician and the first Secretary of State of Illinois. The Fox River played a significant role in the county’s early development, providing water power for mills and industry. The cities of Aurora and Elgin grew into major industrial centers in the 19th and early 20th centuries, and the county has since transitioned into a suburban and commercial hub.
Colleges and Universities:
- Aurora University: A private university offering undergraduate and graduate programs in fields such as business, nursing, and education.
- Elgin Community College: A public community college offering associate degrees, certificates, and workforce training in various fields.
- Judson University: A private Christian university in Elgin, known for its programs in architecture, education, and the arts.
- Northern Illinois University (Aurora Campus): Offers graduate programs and continuing education for professionals.
Major Landmarks:
The Fabyan Windmill in Geneva is a historic Dutch-style windmill that has been restored and is open to the public. The Paramount Theatre in Aurora is a historic venue offering live performances and concerts. The Kane County Cougars, a minor league baseball team, play at Northwestern Medicine Field in Geneva. The Fox River offers numerous recreational opportunities, including kayaking, fishing, and hiking along the Fox River Trail.
6. McHenry County
County Facts:
- Population: Approximately 310,000
- Area Codes: 815, 779
- Zip Codes: 60012–60180
- County Seat: Woodstock
Geography and History:
McHenry County is located in northern Illinois, covering 611 square miles. The county features rolling hills, farmland, and several lakes, including the popular Chain O’Lakes region. The Fox River also runs through parts of the county, providing scenic waterways and recreational opportunities.
Established in 1836, McHenry County was named after Major William McHenry, a figure in the Black Hawk War. The county’s early economy was based on agriculture, with dairy farming being particularly prominent. Over time, the county has developed suburban areas, particularly in the southeast, but much of it remains rural.
Colleges and Universities:
- McHenry County College: A public community college offering associate degrees, certifications, and career training in fields such as healthcare, business, and the arts.
- Aurora University (Woodstock Center): Provides graduate programs in education, business, and social work for McHenry County residents.
- Columbia College of Missouri (Crystal Lake Campus): Offers flexible undergraduate and graduate programs for working adults.
Major Landmarks:
The Woodstock Opera House, located in the county seat, is a historic venue that hosts performances, concerts, and events. The annual McHenry County Fair showcases the area’s agricultural heritage. Moraine Hills State Park, with its scenic trails and fishing areas, is a popular destination for outdoor enthusiasts. The Illinois Railway Museum in Union, the largest railway museum in the U.S., offers visitors a chance to explore historic trains and railcars.
7. Winnebago County
County Facts:
- Population: Approximately 280,000
- Area Codes: 815, 779
- Zip Codes: 61010–61132
- County Seat: Rockford
Geography and History:
Winnebago County is located in northern Illinois along the Wisconsin border, covering 519 square miles. The Rock River runs through the county, including the city of Rockford. The geography includes urban areas, farmland, and natural parks, with a climate typical of the Midwest.
Winnebago County was established in 1836 and named after the Native American Winnebago tribe. Rockford, the county seat, became an industrial powerhouse in the late 19th and early 20th centuries, known for manufacturing heavy machinery and furniture. The county has diversified its economy in recent years, focusing on healthcare, aerospace, and education.
Colleges and Universities:
- Rock Valley College: A public community college offering associate degrees, certifications, and continuing education programs in various fields.
- Rockford University: A private liberal arts university offering undergraduate and graduate programs in business, education, and the sciences.
- University of Illinois College of Medicine (Rockford Campus): Provides medical education and research opportunities, with a focus on rural healthcare.
- Northern Illinois University (Rockford Campus): Offers graduate programs in education, business, and public administration.
Major Landmarks:
Anderson Japanese Gardens in Rockford is one of the top Japanese gardens in the U.S., offering serene landscapes and cultural experiences. The Burpee Museum of Natural History, home to the famous “Jane” dinosaur fossil, is another key attraction. Rock Cut State Park provides opportunities for hiking, camping, and fishing. The Coronado Performing Arts Center, a historic theater in Rockford, hosts concerts, plays, and other events.
8. Madison County
County Facts:
- Population: Approximately 264,000
- Area Codes: 618
- Zip Codes: 62001–62098
- County Seat: Edwardsville
Geography and History:
Madison County is located in southwestern Illinois, just across the Mississippi River from St. Louis, Missouri. The county covers 741 square miles and features a mix of suburban areas, farmland, and riverfront areas. The county’s location near St. Louis has made it a key part of the Metro-East region.
Established in 1812, Madison County was named after President James Madison. The county played a significant role in the early development of Illinois, with Edwardsville being one of the oldest towns in the state. The area’s economy has traditionally been based on agriculture and manufacturing, though it has diversified in recent decades.
Colleges and Universities:
- Southern Illinois University Edwardsville (SIUE): A major public university offering undergraduate and graduate programs in fields such as engineering, business, and healthcare.
- Lewis and Clark Community College: Provides associate degrees, certificates, and workforce development programs for residents of the region.
- McKendree University: Located nearby in Lebanon, this private university offers undergraduate and graduate programs in education, business, and the liberal arts.
Major Landmarks:
The Cahokia Mounds State Historic Site, located in Madison County, is a UNESCO World Heritage Site and the largest pre-Columbian archaeological site north of Mexico. The Lewis and Clark State Historic Site commemorates the start of the famous expedition that explored the western U.S. The National Great Rivers Museum, located near Alton, educates visitors about the Mississippi River’s history and ecology. The county is also home to Edwardsville’s historic downtown area, featuring shops, restaurants, and events year-round.
9. St. Clair County
County Facts:
- Population: Approximately 260,000
- Area Codes: 618
- Zip Codes: 62201–62299
- County Seat: Belleville
Geography and History:
St. Clair County is located in southwestern Illinois, across the Mississippi River from St. Louis, Missouri. Covering 674 square miles, the county features a combination of suburban areas, farmland, and riverfront areas. The region is part of the St. Louis Metro-East area, and its economy is closely linked to the metropolitan area.
St. Clair County was established in 1790, making it one of the oldest counties in Illinois. It was named after General Arthur St. Clair, the first governor of the Northwest Territory. Belleville, the county seat, grew as a coal mining and industrial center in the 19th and early 20th centuries. Today, the county’s economy is based on healthcare, education, and transportation.
Colleges and Universities:
- Southwestern Illinois College (SWIC): A public community college offering associate degrees, certificates, and technical training in various fields.
- McKendree University: A private liberal arts university located nearby in Lebanon, with strong programs in education, business, and health sciences.
- Southern Illinois University Edwardsville (SIUE): Offers graduate programs and continuing education opportunities for St. Clair County residents.
- Lindenwood University (Belleville Campus): Provides undergraduate and graduate programs in business, arts, and sciences.
Major Landmarks:
The Gateway Grizzlies baseball team plays at GCS Ballpark in Sauget, providing family-friendly entertainment. The National Shrine of Our Lady of the Snows, one of the largest outdoor shrines in the U.S., is located in Belleville. Scott Air Force Base, a major military installation, is an important landmark and economic driver for the county. Additionally, the St. Clair County Historical Society operates a museum in Belleville that preserves the region’s history.
10. Sangamon County
County Facts:
- Population: Approximately 195,000
- Area Codes: 217
- Zip Codes: 62563–62794
- County Seat: Springfield
Geography and History:
Sangamon County is located in central Illinois, covering 877 square miles. The county is predominantly flat, with fertile agricultural land and the Sangamon River flowing through it. The region has a continental climate with cold winters and warm summers.
Sangamon County was established in 1821 and named after the Sangamon River. Springfield, the county seat, became the state capital of Illinois in 1837, largely due to the efforts of Abraham Lincoln, who lived in the city for much of his life. Sangamon County’s history is closely tied to Lincoln, and many historical sites related to him are located in the area. Agriculture and government are the primary economic drivers in the region.
Colleges and Universities:
- University of Illinois Springfield (UIS): A public university offering undergraduate and graduate programs in fields such as public administration, business, and the liberal arts.
- Lincoln Land Community College (LLCC): Provides associate degrees, certificates, and workforce training in fields such as healthcare, technology, and business.
- Southern Illinois University School of Medicine: Offers medical education and research opportunities, focusing on rural and underserved populations.
Major Landmarks:
The Abraham Lincoln Presidential Library and Museum is one of the most visited landmarks in Sangamon County, offering an in-depth look at Lincoln’s life and legacy. The Old State Capitol, where Lincoln delivered some of his most famous speeches, is another key site. Lincoln’s home and the Lincoln Tomb, where he is buried, are preserved as national historic sites. The Dana-Thomas House, designed by Frank Lloyd Wright, is an architectural landmark in Springfield.