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|Territory: Mar 1, 1809|
|Statehood: Dec 3, 1818|
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Today’s Illinois counties did not always exist in the present form. They went through many different changes in the space of a few short years. Illinois Counties were first formed while part of the Mississippi Territory, and after that the Illinois Territory.
Illinois Territorial Counties
The Illinois Territory existed from March 1, 1809, until December 3, 1818. There were originally 15 Illinois counties when it gained statehood in 1818.
The State of Illinois entered the union as the 21st state on December 3, 1818.
Illinois Counties Today
Fun Facts about Illinois Counties
Counties by Name
Most Illinois counties were named after
- early American leaders from the American Revolutionary War, Battle of Tippecanoe and the War of 1812.
- natural features
- counties in other states
- early Illinois leaders
- 2 counties are named for Native American tribes
- 1 bears the name of a plant used as a food source by Native Americans
Counties by Year
- St. Clair County was an original County created on June 20, 1790.
- Douglas County was the last county created on March 21, 1859.
County Size Facts
- McLean County (1,184 sq mi) is the largest county in Illinois.
- Putnam County (160 sq mi) is the smallest county in Illinois.
County Population Facts
- Hardin County (4,836) is the least populated county in Illinois.
- Cook County (5,194,675) is the most populated county in Illinois.
Illinois City Facts
Illinois’s 10 largest cities (2010 est.) are:
- Chicago (2,695,598) is in Cook and DuPage Counties
- Aurora (197,899) is in Kane, Will and DuPage Counties
- Rockford (152,871) is in Winnebago County
- Joliet (147,433) is in Will and Kendall Counties
- Naperville (141,853) is in Will and DuPage Counties
- Springfield (116,250) is in Sangamon County
- Peoria (115,007) is in Peoria County
- Elgin (108,188) is in Cook and Kane Counties
- Waukegan (89,078) is in Lake County
- Cicero (83,891) is in Cook County
Boundary Changes of Illinois Counties from 1790-1869
This Interactive Map of Illinois Counties show the historical boundaries, names, organization, and attachments of every county, extinct county and unsuccessful county proposal from 1790 to 1869.
List of Illinois Counties
|County||Date Formed||Parent County||County Seat|
|Bond||1817||Crawford County, Edwards County, and Madison County||Greenville|
|Brown||1839||Schuyler County||Mount Sterling|
|Carroll||1839||Jo Daviess||Mount Carroll|
|Clark||1824||Wayne, Lawrence, Fayette, and Crawford County||Marshall|
|Clay||1824||Washington, Bond, and Fayette County||Louisville|
|Coles||1830||Clark and Edgar County||Charleston|
|De Kalb||1837||Kane County||Sycamore|
|Douglas||1839||Macon and McLean County||Tuscola|
|Edwards||1814||Gallatin County and Madison County||Albion|
|Effingham||1831||Fayette and Crawford County||Effingham|
|Fayette||1821||Bond, Wayne, Clark, Jefferson, and Crawford County||Vandalia|
|Franklin||1818||White County and Gallatin County||Benton|
|Jackson||1816||Randolph County and Johnson County||Murphysboro|
|Jasper||1831||Clay and Crawford County||Newton|
|Jo Daviess||1819||Edwards and White County||Galena|
|Jefferson||1839||Greene County||Mount Vernon|
|Jersey||1827||Henry, Mercer, and Putnam County||Jerseyville|
|Kankakee||1853||Iroquois and Will County||Kankakee|
|Knox||1841||LaSalle and Kane County||Yorkville|
|Lawrence||1831||Putnam and Tazewell County||Lawrenceville|
|Lee||1821||Crawford and Edwards County||Dixon|
|Logan||1837||LaSalle and McLean County||Lincoln|
|La Salle||1839||Sangamon County||Ottawa|
|McHenry||1812||St. Clair County and Randolph County||Woodstock|
|McLean||1823||Fayette and Jefferson County||Bloomington|
|Menard||1841||Tazewell and Menard County||Petersburg|
|Mercer||1843||Pope and Johnson County||Aledo|
|Moultrie||1836||Cook and LaSalle County||Sullivan|
|Massac||1816||Randolph County and St. Clair County||Metropolis|
|Marshall||1821||Bond and Madison County||Lacon|
|Montgomery||1843||Shelby and Macon County||Hillsboro|
|Perry||1827||Randolph and Jackson County||Pinckneyville|
|Piatt||1841||DeWitt and Macon County||Monticello|
|Pike||1821||Madison, Bond, and Clark County||Pittsfield|
|Pope||1816||Gallatin and Johnson County||Golconda|
|Pulaski||1843||Alexander and Johnson County||Mound City|
|Randolph||1795||St. Clair County||Chester|
|Richland||1841||Clay and Lawrence County||Olney|
|Rock Island||1831||Jo Daviess County||Rock Island|
|Sangamon||1821||Madison and Bond County||Springfield|
|St. Clair||1790||original two counties||Belleville|
|Schuyler||1825||Pike and Fulton Counties||Rushville|
|Stark||1839||Knox and Putnam County||Toulon|
|Stephenson||1837||Jo Daviess and Winnebago County||Freeport|
|Wabash||1824||Edwards County||Mount Carmel|
|Washington||1818||St. Clair County||Nashville|
|Winnebago||1836||Jo Daviess and Henry County||Rockford|
|Woodford||1836||Cook and Iroquois County||Eureka|
|White||1841||Tazewell and McLean County||Carmi|
List of Old Former / Extinct Illinois Counties
Illinois contains some counties that no longer exist because they were discontinued, renamed or merged with another county. These are important for genealogy research purposes.
The below counties formerly within the area of the State of Illinois no longer exist:
Dane County, Illinois
Hignland County, Illinois
Created on February 27, 1847 from Marquette County. Highland County was merged into Adams County on December 31, 1848.
Marquette County, Illinois
Created on February 1, 1843 from Adams County. Marquette County was renamed to Hignland County on February 27, 1847.