DeWitt County is a county located in the U.S. state of Illinois. As of the 2020 census, the population was 15,516. Its county seat is Clinton. The county was formed on March 1, 1839, from Macon and McLean counties. The county was named in honor of the seventh Governor of New York State, DeWitt Clinton.
Winnebago County is a county located in the U.S. state of Illinois. According to the 2020 census, it had a population of 285,350 making it the seventh most populous county in Illinois behind Cook County and its five surrounding collar counties. Its county seat is Rockford. Winnebago County is the central county of the Rockford Metropolitan Statistical Area.
Warren County is a county in the U.S. state of Illinois. According to the 2020 census, it had a population of 16,835. Its county seat is Monmouth.
Tazewell County is a county in the U.S. state of Illinois. According to the 2020 census, it had a population of 131,343. Its county seat and largest city is Pekin. It is pronounced with a short "a", to rhyme with "razz" rather than "raze."
St. Clair County is the ninth most populous county in Illinois. Located directly east of St. Louis, the county is part of the Metro East region of the Greater St. Louis metropolitan area in southern Illinois. As of the 2020 United States census, St. Clair County had a population of 257,400, making it the third most populous county in Illinois outside the Chicago metropolitan area. Belleville is the county’s seat and largest city.
Shelby County is a county located in the U.S. state of Illinois. According to the 2020 census, it had a population of 20,990. Its county seat is Shelbyville.
Rock Island County is a county located in the U.S. state of Illinois, bounded on the west by the Mississippi River. According to the 2020 census, it had a population of 144,672. Its county seat is Rock Island; its largest city is neighboring Moline. Rock Island County is one of the four counties that make up the Davenport-Moline-Rock Island, IA-IL Metropolitan Statistical Area.
Pulaski County is a county located in the U.S. state of Illinois. According to the 2020 census, it had a population of 5,193. Its county seat is Mound City. Its largest city is Mounds. It is located along the Ohio River in the southwestern portion of the state, known locally as "Little Egypt".
Livingston County is a county located in the U.S. state of Illinois. According to the 2020 census, it has a population of 35,815. Its county seat is Pontiac. Livingston County comprises the Pontiac, IL Micropolitan Statistical Area, which is combined with the Bloomington–Normal metropolitan statistical area as the Bloomington-Pontiac, IL Combined Statistical Area in upper portion of Central Illinois.
Lawrence County is the easternmost county in the U.S. state of Illinois. At the 2020 census, the population was 15,280. Its county seat is Lawrenceville.
Knox County is a county in the U.S. state of Illinois. According to the 2020 census, it had a population of 49,967. Its county seat is Galesburg.
Kankakee County is a county located in the U.S. state of Illinois. According to the 2020 census, it has a population of 107,502. Its county seat is Kankakee. Kankakee County comprises the Kankakee, IL Metropolitan Statistical Area.
Johnson County is a county in the U.S. state of Illinois. According to the 2020 census, it has a population of 13,308. Its county seat is Vienna. It is located in the southern portion of Illinois known locally as "Little Egypt".
Hamilton County is a county located in the U.S. state of Illinois. At the 2020 census, its population was 7,993. Its county seat is McLeansboro. It is located in the southern portion of the state known locally as "Little Egypt".
Effingham County is located in the south central part of the U.S. state Illinois. As of the 2020 census, the population was 34,668. Its county seat and largest city is Effingham. Some other cities in Effingham County, Illinois include Altamont, Teutopolis, Beecher City, Montrose, Dieterich, Shumway, Watson, Mason, and Edgewood. Effingham County comprises the Effingham, IL Micropolitan Statistical Area.
Cumberland County is a county located in the U.S. state of Illinois. As of the 2020 census, the population was 10,450. Its county seat is Toledo.
Christian County is a county located in the U.S. state of Illinois. As of the 2020 census, the population was 34,032. Its county seat is Taylorville.
Brown County is a county located in the U.S. state of Illinois. As of the 2020 census, the population was 6,244. Its county seat is Mount Sterling.
Alexander County is the southernmost and southwesternmost county in the U.S. state of Illinois. As of the 2020 census, the population was 5,240. Its county seat is Cairo and its western boundary is formed by the Mississippi River.
The U.S. State of Illinois currently has 43 statistical areas that have been delineated by the Office of Management and Budget (OMB). On March 6, 2020, the OMB delineated 11 combined statistical areas, 13 metropolitan statistical areas, and 19 micropolitan statistical areas in Illinois.
United States 
Illinois 
St. Clair 
