| The Political Divisions of Illinois |
|---|
| County Name | Date of Formation | Parent County | County Seat |
| Adams | 1825 | Pike | Quincy |
| Alexander | 1819 | Union | Cairo |
| Bond | 1818 | Madison | Greenville |
| Boone | 1836 | Winnebago | Belvidere |
| Brown | 1837 | Schuyler | Mount Sterling |
| Bureau | 1837 | Putnam | Princeton |
| Calhoun | 1825 | Pike | Hardin |
| Carroll | 1839 | Jo Daviess | Mount Carroll |
| Cass | 1837 | Morgan | Virginia |
| Champaign | 1833 | Vermilion | Urbana |
| Christian | 1839 | Dane (Formed from Montgomery, Sangamon, Shelby) | Taylorville |
| Clark | 1819 | Crawford | Marshall |
| Clay | 1824 | Crawford, Fayette, Wayne | Louisville |
| Clinton | 1824 | Bond, Washington | Carlyle |
| Coles | 1830 | Clark, Edgar | Charleston |
| Cook | 1831 | Putnam | Chicago |
| Crawford | 1816 | Edwards | Robinson |
| Cumberland | 1843 | Coles | Toledo |
| Dane | 1839 | Montgomery, Sangamon, Shelby | Defunct, now CHRISTIAN |
| DeKalb | 1837 | Kane | Sycamore |
| DeWitt | 1839 | Macon, McLean | Perry |
| Douglas | 1859 | Coles | Tuscola |
| DuPage | 1839 | Cook | Wheaton |
| Edgar | 1823 | Clark | Paris |
| Edwards | 1814 | Gallatin, Madison | Albion |
| Effingham | 1831 | Crawford, Fayette | Effingham |
| Fayette | 1821 | Bond, Clark, Crawford, Jefferson | Vandalia |
| Ford | 1859 | unorganized | Paxton |
| Franklin | 1818 | Galatin, White | Benton |
| Fulton | 1823 | Pike | Lewistown |
| Gallatin | 1812 | Randolph | Shawneetown |
| Greene | 1821 | Madison | Carrollton |
| Grundy | 1841 | LaSalle | Morris |
| Hamilton | 1821 | White | McLeansboro |
| Hancock | 1825 | Pike | Carthage |
| Hardin | 1839 | Gallatin, Pope | Elizabethtown |
| Henderson | 1841 | Warren | Oquawka |
| Henry | 1825 | unorganized | Cambridge |
| Iroquis | 1833 | unorganized | Watseka |
| Jackson | 1816 | Johnson, Randolph | Murphysboro |
| Jasper | 1831 | Clay, Crawford | Newton |
| Jefferson | 1819 | Edwards, White | Mount Vernon |
| Jersey | 1839 | Greene | Jerseyville |
| JoDaviess | 1827 | Henry, Putnam | Galena |
| Johnson | 1812 | Randolph | Vienna |
| Kane | 1836 | unorganized | Geneva |
| Kankakee | 1853 | Ford, Iroquis, Will | Kankakee |
| Kendall | 1841 | LaSalle, Kane | Yorkville |
| Knox | 1825 | unorganized, Fulton, Henry | Galesburg |
| Lake | 1839 | McHenry | Waukegan |
| LaSalle | 1831 | Putnam, unorganized | Ottawa |
| Lawrence | 1821 | Crawford, Edwards | Lawrenceville |
| Lee | 1839 | Ogle | Dixon |
| Livingston | 1837 | LaSalle, McLean, unorganized | Pontiac |
| Logan | 1839 | McLean, Sangamon, Tazewell | Lincoln |
| Macon | 1829 | unorganized | Decatur |
| Macoupin | 1829 | unorganized, Madison | Carlinville |
| Madison | 1812 | St. Clair | Edwardsville |
| Marion | 1823 | Fayette, Jefferson | Salem |
| Marshall | 1839 | Putnam, LaSalle | Lacon |
| Mason | 1841 | Menard, Tazeweklk | Havana |
| Massac | 1843 | Johnson, Pope | Metropolis |
| McDonough | 1826 | Schuyler | Macomb |
| McHenry | 1836 | Cook, unorganized | Woodstock |
| McLean | 1830 | Tazewell, unorganized | Bloomington |
| Menard | 1839 | Sangamon | Petersburg |
| Mercer | 1825 | unorganized | Aledo |
| Monroe | 1816 | Randolph, St. Clair | Waterloo |
| Montgomery | 1821 | Bond, Madison | Hillsboro |
| Morgan | 1823 | unorganized, Sangamon | Jacksonville |
| Moultrie | 1843 | Macon, Shelby | Sullivan |
| Ogle | 1836 | Jo Daviess, unorganized | Oregon |
| Peoria | 1825 | Fulton, unorganized | Peoria |
| Perry | 1827 | Jackson, Randolph | Pickneyville |
| Piatt | 1841 | DeWitt, Macon | Monticello |
| Pike | 1821 | Madison | Pittsfield |
| Pope | 1816 | Gallatin, Johnson | Golconda |
| Pulaski | 1843 | Alexander, Johnson | Mound City |
| Putnam | 1825 | unorganized | Hennepin |
| Randolph | 1795 | St. Clair, Northwest Territory | Chester |
| Richland | 1841 | Clay, Lowrence | Olney |
| Rock Island | 1831 | Jo Daviess | Rock Island |
| Saline | 1847 | Gallatin | Harrisburg |
| Sangamon | 1821 | Bond, Madison | Springfield |
| Schuyler | 1825 | Pike, unorganized | Rushville |
| Scott | 189 | Morgan | Winchester |
| Shelby | 1827 | Fayette | Shelbyville |
| Stark | 1839 | Knox, Putnam | Toulon |
| St. Clair | 1790 | Northwest Territory | Belleville |
| Stephenson | 1837 | Jo Daviess, Winnebago | Freeport |
| Tazewell | 1827 | unorganized, Fayette | Pekin |
| Union | 1818 | Johnson, Jackson | Jonesboro |
| Vermilion | 1826 | unorganized | Danville |
| Wabash | 1824 | Edwards | Mout Carmel |
| Warren | 1825 | unorganized | Monmouoth |
| Washington | 1818 | St. Clair | Nashville |
| Wayne | 1819 | Edwards | Fairfield |
| White | 1815 | Madison | Carmi |
| Whiteside | 1836 | Jo Daviess, Henry | Morrison |
| Will | 1836 | Cook, Iroquois | Joliet |
| Williamson | 1839 | Franklin | Marion |
| Winnebago | 1836 | Jo Daviess, unorganized | Rockford |
| Woodford | 1841 | McLean, Tazewell | Eureka
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