List of counties in Illinois facts for kids

Kids Encyclopedia Facts
Counties of Illinois
Location State of Illinois
Number 102
Populations 4,836 (Hardin) – 5,194,675 (Cook)
Areas 160 square miles (410 km2) (Putnam) – 1,184 square miles (3,070 km2) (McLean)
Government County government
Subdivisions 261 Precincts
1,433 Townships
See also: List of United States counties and county equivalents

There are 102 counties in the state of Illinois.

Most counties in Illinois were named after early American leaders, especially of the American Revolutionary War, as well as soldiers from the Battle of Tippecanoe and the War of 1812. Some are named after natural features or counties in other states. Some are named for early Illinois leaders. Two counties are named for Native American tribes, and one bears the name of a plant used as a food source by Native Americans.

While it does have a city, Illinois does not have a Lincoln County named after its favorite son, Abraham Lincoln; it does, however, have a Douglas County (founded 1859) named after his political rival Stephen A. Douglas. It also has Calhoun County (founded 1825), named after John C. Calhoun, outspoken for his pro-slavery and pro-southern views in the years preceding the American Civil War. Several of the counties are named after Southerners, reflecting the fact that Illinois was for a short time part of Virginia, and settled in its early years by many Southerners. No counties are named after Northern heroes of the Civil War, mainly because the counties were all named before that war. The state does have a Lee County named after the family of Robert E. Lee, who at one time served in Illinois. Illinois also has two counties named after the same person, New York governor DeWitt Clinton (this may be unusual, but it is not unprecedented since Virginia has had two counties named after Patrick Henry since 1790).

Information on the FIPS county code, county seat, year of establishment, origin, etymology, population, area and map of each county is included in the table below.

Illinois's postal abbreviation is IL and its FIPS state code is 17.


Note: the links in the FIPS County Code column are to the Census Bureau info page for that county.


County seat



Adams County 001 Quincy 1825 Pike County John Quincy Adams (1767–1848), sixth President of the United States &&&&&&&&&&067103.&&&&&067,103 &&&&&&&&&&&&0857.&&&&&0857 sq mi
(&&&&&&&&&&&02220.&&&&&02,220 km²)
State map highlighting Adams County
Alexander County 003 Cairo 1819 Union County William M. Alexander, settler and state representative in the Illinois General Assembly &&&&&&&&&&&08238.&&&&&08,238 &&&&&&&&&&&&0236.&&&&&0236 sq mi
(&&&&&&&&&&&&0611.&&&&&0611 km²)
State map highlighting Alexander County
Bond County 005 Greenville 1817 Crawford County, Edwards County, and Madison County Shadrach Bond (1773–1832), first Governor of Illinois &&&&&&&&&&017768.&&&&&017,768 &&&&&&&&&&&&0380.&&&&&0380 sq mi
(&&&&&&&&&&&&0984.&&&&&0984 km²)
Boone County 007 Belvidere 1837 Winnebago County Daniel Boone (1734–1820), trailblazer of the Wilderness Road in Kentucky &&&&&&&&&&054165.&&&&&054,165 &&&&&&&&&&&&0281.&&&&&0281 sq mi
(&&&&&&&&&&&&0728.&&&&&0728 km²)
State map highlighting Boone County
Brown County 009 Mount Sterling 1839 Schuyler County Jacob Brown (1775–1828), successful War of 1812 army officer responsible for Great Lakes defenses &&&&&&&&&&&06937.&&&&&06,937 &&&&&&&&&&&&0306.&&&&&0306 sq mi
(&&&&&&&&&&&&0793.&&&&&0793 km²)
Bureau County 011 Princeton 1837 Putnam County Pierre de Bureo, Frenchman, North American fur trader &&&&&&&&&&034978.&&&&&034,978 &&&&&&&&&&&&0869.&&&&&0869 sq mi
(&&&&&&&&&&&02251.&&&&&02,251 km²)
State map highlighting Bureau County
Calhoun County 013 Hardin 1825 Pike County John C. Calhoun (1782–1850), South Carolina senator and seventh Vice President of the United States &&&&&&&&&&&05089.&&&&&05,089 &&&&&&&&&&&&0254.&&&&&0254 sq mi
(&&&&&&&&&&&&0658.&&&&&0658 km²)
State map highlighting Calhoun County
Carroll County 015 Mount Carroll 1839 Jo Daviess Charles Carroll of Carrollton (1737–1832), signed the Declaration of Independence on behalf of Maryland &&&&&&&&&&015387.&&&&&015,387 &&&&&&&&&&&&0444.&&&&&0444 sq mi
(&&&&&&&&&&&01150.&&&&&01,150 km²)
State map highlighting Carroll County
Cass County 017 Virginia 1837 Morgan County Lewis Cass (1782–1866), second governor of Michigan Territory, fourteenth United States Secretary of War &&&&&&&&&&013642.&&&&&013,642 &&&&&&&&&&&&0376.&&&&&0376 sq mi
(&&&&&&&&&&&&0974.&&&&&0974 km²)
Champaign County 019 Urbana 1833 Vermilion County Champaign County, Ohio, which took its name from the French for "open level country" &&&&&&&&&0201081.&&&&&0201,081 &&&&&&&&&&&&0997.&&&&&0997 sq mi
(&&&&&&&&&&&02582.&&&&&02,582 km²)
State map highlighting Champaign County
Christian County 021 Taylorville 1839 Sangamon County Christian County, Kentucky, which was itself named after Colonel William Christian &&&&&&&&&&034800.&&&&&034,800 &&&&&&&&&&&&0709.&&&&&0709 sq mi
(&&&&&&&&&&&01836.&&&&&01,836 km²)
Clark County 023 Marshall 1819 Crawford County George Rogers Clark (1752–1818), highest-ranking officer in the Northwest Territory during the American Revolution &&&&&&&&&&016335.&&&&&016,335 &&&&&&&&&&&&0502.&&&&&0502 sq mi
(&&&&&&&&&&&01300.&&&&&01,300 km²)
State map highlighting Clark County
Clay County 025 Louisville 1824 Wayne, Lawrence, Fayette, and Crawford County Henry Clay (1777–1852), Kentucky legislator who negotiated the Missouri Compromise &&&&&&&&&&013815.&&&&&013,815 &&&&&&&&&&&&0469.&&&&&0469 sq mi
(&&&&&&&&&&&01215.&&&&&01,215 km²)
Clinton County 027 Carlyle 1824 Washington, Bond, and Fayette County DeWitt Clinton (1769–1828), Governor of New York, responsible for the construction of the Erie Canal &&&&&&&&&&037762.&&&&&037,762 &&&&&&&&&&&&0474.&&&&&0474 sq mi
(&&&&&&&&&&&01228.&&&&&01,228 km²)
Coles County 029 Charleston 1830 Clark and Edgar County Edward Coles (1786–1868), second Governor of Illinois, responsible for the abolition of slavery in Illinois &&&&&&&&&&053873.&&&&&053,873 &&&&&&&&&&&&0508.&&&&&0508 sq mi
(&&&&&&&&&&&01316.&&&&&01,316 km²)
State map highlighting Coles County
Cook County 031 Chicago 1831 Putnam County Daniel Pope Cook (1794–1827), politician and first Attorney General of Illinois &&&&&&&&05194675.&&&&&05,194,675 &&&&&&&&&&&&0946.&&&&&0946 sq mi
(&&&&&&&&&&&02450.&&&&&02,450 km²)
State map highlighting Cook County
Crawford County 033 Robinson 1816 Edwards County William H. Crawford (1772–1834), ninth United States Secretary of War, seventh Secretary of the Treasury &&&&&&&&&&019817.&&&&&019,817 &&&&&&&&&&&&0444.&&&&&0444 sq mi
(&&&&&&&&&&&01150.&&&&&01,150 km²)
State map highlighting Crawford County
Cumberland County 035 Toledo 1843 Coles County Disputed: Cumberland Road, which entered the county; Cumberland, Maryland; or Cumberland River in Kentucky &&&&&&&&&&011048.&&&&&011,048 &&&&&&&&&&&&0346.&&&&&0346 sq mi
(&&&&&&&&&&&&0896.&&&&&0896 km²)
DeKalb County 037 Sycamore 1837 Kane County Johann de Kalb (1721–1780), German soldier in the Continental Army who fought alongside Gilbert du Motier, marquis de Lafayette &&&&&&&&&0105160.&&&&&0105,160 &&&&&&&&&&&&0634.&&&&&0634 sq mi
(&&&&&&&&&&&01642.&&&&&01,642 km²)
State map highlighting DeKalb County
DeWitt County 039 Clinton 1839 Macon and McLean County DeWitt Clinton (1769–1828), Governor of New York, responsible for the construction of the Erie Canal &&&&&&&&&&016561.&&&&&016,561 &&&&&&&&&&&&0398.&&&&&0398 sq mi
(&&&&&&&&&&&01031.&&&&&01,031 km²)
State map highlighting DeWitt County
Douglas County 041 Tuscola 1859 Coles County Stephen A. Douglas (1813–61), prominent Illinois Democrat who engaged in debates with Abraham Lincoln &&&&&&&&&&019980.&&&&&019,980 &&&&&&&&&&&&0417.&&&&&0417 sq mi
(&&&&&&&&&&&01080.&&&&&01,080 km²)
DuPage County 043 Wheaton 1839 Cook County DuPage River &&&&&&&&&0916924.&&&&&0916,924 &&&&&&&&&&&&0334.&&&&&0334 sq mi
(&&&&&&&&&&&&0865.&&&&&0865 km²)
State map highlighting DuPage County
Edgar County 045 Paris 1823 Clark County John Edgar (c. 1750–1832), Illinois delegate to the Northwest Territory legislature; at the time, wealthiest man in Illinois &&&&&&&&&&018576.&&&&&018,576 &&&&&&&&&&&&0624.&&&&&0624 sq mi
(&&&&&&&&&&&01616.&&&&&01,616 km²)
State map highlighting Edgar County
Edwards County 047 Albion 1814 Gallatin County and Madison County Ninian Edwards (1775–1833), third Governor of the State of Illinois and only governor of the Illinois Territory &&&&&&&&&&&06721.&&&&&06,721 &&&&&&&&&&&&0222.&&&&&0222 sq mi
(&&&&&&&&&&&&0575.&&&&&0575 km²)
Effingham County 049 Effingham 1831 Fayette and Crawford County Thomas Howard, 3rd Earl of Effingham, military officer who resigned from the British Army to avoid fighting the American colonies &&&&&&&&&&034242.&&&&&034,242 &&&&&&&&&&&&0479.&&&&&0479 sq mi
(&&&&&&&&&&&01241.&&&&&01,241 km²)
Fayette County 051 Vandalia 1821 Bond, Wayne, Clark, Jefferson, and Crawford County Gilbert du Motier, marquis de Lafayette (1757–1834), French military officer who was a key factor in the American and French Revolutions. &&&&&&&&&&022140.&&&&&022,140 &&&&&&&&&&&&0716.&&&&&0716 sq mi
(&&&&&&&&&&&01854.&&&&&01,854 km²)
Ford County 053 Paxton 1859 Vermilion County Thomas Ford (1800–50), eighth Governor of Illinois; served during the Illinois Mormon War &&&&&&&&&&014081.&&&&&014,081 &&&&&&&&&&&&0486.&&&&&0486 sq mi
(&&&&&&&&&&&01259.&&&&&01,259 km²)
Franklin County 055 Benton 1818 White County and Gallatin County Benjamin Franklin (1706–90), prolific writer, inventor, and politician; key factor in the American Revolution &&&&&&&&&&039561.&&&&&039,561 &&&&&&&&&&&&0412.&&&&&0412 sq mi
(&&&&&&&&&&&01067.&&&&&01,067 km²)
Fulton County 057 Lewistown 1823 Pike County Robert Fulton (1765–1815), inventor of the steamboat &&&&&&&&&&037069.&&&&&037,069 &&&&&&&&&&&&0866.&&&&&0866 sq mi
(&&&&&&&&&&&02243.&&&&&02,243 km²)
State map highlighting Fulton County
Gallatin County 059 Shawneetown 1812 Randolph County Albert Gallatin (1761–1849), fourth and longest-serving United States Secretary of the Treasury &&&&&&&&&&&05589.&&&&&05,589 &&&&&&&&&&&&0324.&&&&&0324 sq mi
(&&&&&&&&&&&&0839.&&&&&0839 km²)
State map highlighting Gallatin County
Greene County 061 Carrollton 1821 Madison County Nathanael Greene (1742–86), major general in the Continental Army &&&&&&&&&&013886.&&&&&013,886 &&&&&&&&&&&&0543.&&&&&0543 sq mi
(&&&&&&&&&&&01406.&&&&&01,406 km²)
State map highlighting Greene County
Grundy County 063 Morris 1841 LaSalle County Felix Grundy (1777–1840), Tennessean senator who served as the thirteenth United States Attorney General &&&&&&&&&&050063.&&&&&050,063 &&&&&&&&&&&&0420.&&&&&0420 sq mi
(&&&&&&&&&&&01088.&&&&&01,088 km²)
State map highlighting Grundy County
Hamilton County 065 McLeansboro 1821 White County Alexander Hamilton (1755–1804), first United States Secretary of the Treasury &&&&&&&&&&&08457.&&&&&08,457 &&&&&&&&&&&&0435.&&&&&0435 sq mi
(&&&&&&&&&&&01127.&&&&&01,127 km²)
Hancock County 067 Carthage 1825 Adams County John Hancock (1737–93), first governor of the Massachusetts colony and president of the Second Continental Congress &&&&&&&&&&019104.&&&&&019,104 &&&&&&&&&&&&0795.&&&&&0795 sq mi
(&&&&&&&&&&&02059.&&&&&02,059 km²)
State map highlighting Hancock County
Hardin County 069 Elizabethtown 1839 Pope County Hardin County, Kentucky, which was itself named after John Hardin &&&&&&&&&&&04320.&&&&&04,320 &&&&&&&&&&&&0178.&&&&&0178 sq mi
(&&&&&&&&&&&&0461.&&&&&0461 km²)
Henderson County 071 Oquawka 1841 Warren County Henderson County, Kentucky, which was itself named after Richard Henderson &&&&&&&&&&&07331.&&&&&07,331 &&&&&&&&&&&&0379.&&&&&0379 sq mi
(&&&&&&&&&&&&0982.&&&&&0982 km²)
Henry County 073 Cambridge 1825 Fulton County Patrick Henry (1736-99), American Revolutionary War figure; first and sixth Governor of Virginia &&&&&&&&&&050486.&&&&&050,486 &&&&&&&&&&&&0823.&&&&&0823 sq mi
(&&&&&&&&&&&02132.&&&&&02,132 km²)
State map highlighting Henry County
Iroquois County 075 Watseka 1833 Vermilion County Iroquois Native Americans &&&&&&&&&&029718.&&&&&029,718 &&&&&&&&&&&01116.&&&&&01,116 sq mi
(&&&&&&&&&&&02890.&&&&&02,890 km²)
State map highlighting Iroquois County
Jackson County 077 Murphysboro 1816 Randolph County and Johnson County Andrew Jackson (1767–1845), seventh President of the United States, United States Senator from Tennessee, and general in the War of 1812 &&&&&&&&&&060218.&&&&&060,218 &&&&&&&&&&&&0588.&&&&&0588 sq mi
(&&&&&&&&&&&01523.&&&&&01,523 km²)
State map highlighting Jackson County
Jasper County 079 Newton 1831 Clay and Crawford County Sgt. William Jasper (c. 1750-79), American Revolutionary War soldier popularized by Parson Weems &&&&&&&&&&&09698.&&&&&09,698 &&&&&&&&&&&&0494.&&&&&0494 sq mi
(&&&&&&&&&&&01279.&&&&&01,279 km²)
Jefferson County 081 Mount Vernon 1819 Edwards and White County Thomas Jefferson (1743–1826), third President of the United States, second Vice President of the United States, Governor of Virginia, and one of the foremost Founding Fathers of the United States &&&&&&&&&&038827.&&&&&038,827 &&&&&&&&&&&&0571.&&&&&0571 sq mi
(&&&&&&&&&&&01479.&&&&&01,479 km²)
Jersey County 083 Jerseyville 1839 Greene County State of New Jersey, from which many early settlers hailed &&&&&&&&&&022985.&&&&&022,985 &&&&&&&&&&&&0369.&&&&&0369 sq mi
(&&&&&&&&&&&&0956.&&&&&0956 km²)
State map highlighting Jersey County
Jo Daviess County 085 Galena 1827 Henry, Mercer, and Putnam County Joseph Hamilton Daveiss (1774–1811), commander of the Indiana Dragoons at the Battle of Tippecanoe &&&&&&&&&&022678.&&&&&022,678 &&&&&&&&&&&&0601.&&&&&0601 sq mi
(&&&&&&&&&&&01557.&&&&&01,557 km²)
State map highlighting Jo Daviess County
Johnson County 087 Vienna 1812 Randolph County Richard Mentor Johnson (abt. 1780-1850), ninth Vice President of the United States and United States Senator from Kentucky &&&&&&&&&&012582.&&&&&012,582 &&&&&&&&&&&&0346.&&&&&0346 sq mi
(&&&&&&&&&&&&0896.&&&&&0896 km²)
Kane County 089 Geneva 1836 LaSalle County Elias Kane (1794–1835), United States Senator from Illinois &&&&&&&&&0515269.&&&&&0515,269 &&&&&&&&&&&&0521.&&&&&0521 sq mi
(&&&&&&&&&&&01349.&&&&&01,349 km²)
State map highlighting Kane County
Kankakee County 091 Kankakee 1853 Iroquois and Will County Kankakee River &&&&&&&&&0113449.&&&&&0113,449 &&&&&&&&&&&&0678.&&&&&0678 sq mi
(&&&&&&&&&&&01756.&&&&&01,756 km²)
State map highlighting Kankakee County
Kendall County 093 Yorkville 1841 LaSalle and Kane County Amos Kendall (1789–1869), United States Postmaster General under Presidents Andrew Jackson and Martin Van Buren &&&&&&&&&0114736.&&&&&0114,736 &&&&&&&&&&&&0321.&&&&&0321 sq mi
(&&&&&&&&&&&&0831.&&&&&0831 km²)
State map highlighting Kendall County
Knox County 095 Galesburg 1825 Fulton County Gen. Henry Knox (1750–1806), American Revolutionary War general and first United States Secretary of War &&&&&&&&&&052919.&&&&&052,919 &&&&&&&&&&&&0716.&&&&&0716 sq mi
(&&&&&&&&&&&01854.&&&&&01,854 km²)
State map highlighting Knox County
Lake County 097 Waukegan 1839 McHenry County Lake Michigan &&&&&&&&&0703462.&&&&&0703,462 &&&&&&&&&&&&0448.&&&&&0448 sq mi
(&&&&&&&&&&&01160.&&&&&01,160 km²)
State map highlighting Lake County
LaSalle County 099 Ottawa 1831 Putnam and Tazewell County Sieur de la Salle (1643-87), French explorer of the Great Lakes &&&&&&&&&0113924.&&&&&0113,924 &&&&&&&&&&&01135.&&&&&01,135 sq mi
(&&&&&&&&&&&02940.&&&&&02,940 km²)
State map highlighting LaSalle County
Lawrence County 101 Lawrenceville 1821 Crawford and Edwards County Capt. James Lawrence (1781–1813), commander of the USS Chesapeake in the War of 1812. Famous for his command "Don't give up the ship!" &&&&&&&&&&016833.&&&&&016,833 &&&&&&&&&&&&0372.&&&&&0372 sq mi
(&&&&&&&&&&&&0963.&&&&&0963 km²)
Lee County 103 Dixon 1839 Ogle County "Light Horse" Henry Lee III (1756–1818), American Revolutionary War officer and ninth Governor of Virginia &&&&&&&&&&036031.&&&&&036,031 &&&&&&&&&&&&0725.&&&&&0725 sq mi
(&&&&&&&&&&&01878.&&&&&01,878 km²)
State map highlighting Lee County
Livingston County 105 Pontiac 1837 LaSalle and McLean County Edward Livingston (1764–1836), prominent jurist, Congressman from New York and Louisiana, and U.S. Secretary of State from 1831-33 &&&&&&&&&&038950.&&&&&038,950 &&&&&&&&&&&01044.&&&&&01,044 sq mi
(&&&&&&&&&&&02704.&&&&&02,704 km²)
State map highlighting Livingston County
Logan County 107 Lincoln 1839 Sangamon County John Logan, country doctor and early settler, and the father of John A. Logan &&&&&&&&&&030305.&&&&&030,305 &&&&&&&&&&&&0618.&&&&&0618 sq mi
(&&&&&&&&&&&01601.&&&&&01,601 km²)
State map highlighting Logan County
Macon County 115 Decatur 1829 Shelby County Nathaniel Macon (1758–1837), sixth Speaker of the United States House of Representatives and United States Senator from North Carolina &&&&&&&&&0110768.&&&&&0110,768 &&&&&&&&&&&&0581.&&&&&0581 sq mi
(&&&&&&&&&&&01505.&&&&&01,505 km²)
State map highlighting Macon County
Macoupin County 117 Carlinville 1829 Greene County Native American word macoupin, meaning "American lotus" &&&&&&&&&&047765.&&&&&047,765 &&&&&&&&&&&&0864.&&&&&0864 sq mi
(&&&&&&&&&&&02238.&&&&&02,238 km²)
State map highlighting Macoupin County
Madison County 119 Edwardsville 1812 St. Clair County and Randolph County James Madison (1751–1836), fourth President of the United States and principal author of the Constitution of the United States &&&&&&&&&0269282.&&&&&0269,282 &&&&&&&&&&&&0725.&&&&&0725 sq mi
(&&&&&&&&&&&01878.&&&&&01,878 km²)
State map highlighting Madison County
Marion County 121 Salem 1823 Fayette and Jefferson County Francis Marion (c. 1732-95), general in the American Revolutionary War known as "The Swamp Fox" &&&&&&&&&&039437.&&&&&039,437 &&&&&&&&&&&&0572.&&&&&0572 sq mi
(&&&&&&&&&&&01481.&&&&&01,481 km²)
State map highlighting Marion County
Marshall County 123 Lacon 1839 Putnam County John Marshall (1755–1835), fourth and longest-serving Chief Justice of the United States, wrote opinion in Marbury v. Madison establishing the principle of judicial review &&&&&&&&&&012640.&&&&&012,640 &&&&&&&&&&&&0386.&&&&&0386 sq mi
(&&&&&&&&&&&01000.&&&&&01,000 km²)
Mason County 125 Havana 1841 Tazewell and Menard County Named after Mason County, Kentucky, itself named after George Mason &&&&&&&&&&014666.&&&&&014,666 &&&&&&&&&&&&0539.&&&&&0539 sq mi
(&&&&&&&&&&&01396.&&&&&01,396 km²)
Massac County 127 Metropolis 1843 Pope and Johnson County Fort Massac, a colonial-era fort on the Ohio River &&&&&&&&&&015429.&&&&&015,429 &&&&&&&&&&&&0239.&&&&&0239 sq mi
(&&&&&&&&&&&&0619.&&&&&0619 km²)
McDonough County 109 Macomb 1826 Schuyler County Commodore Thomas Macdonough (1783–1825), commander of American naval forces at the Battle of Plattsburgh &&&&&&&&&&032612.&&&&&032,612 &&&&&&&&&&&&0589.&&&&&0589 sq mi
(&&&&&&&&&&&01526.&&&&&01,526 km²)
State map highlighting McDonough County
McHenry County 111 Woodstock 1836 Cook and LaSalle County Major William McHenry (c. 1771 – 1835), officer in during several campaigns against Native Americans and member of the Illinois legislature &&&&&&&&&0308760.&&&&&0308,760 &&&&&&&&&&&&0604.&&&&&0604 sq mi
(&&&&&&&&&&&01564.&&&&&01,564 km²)
State map highlighting McHenry County
McLean County 113 Bloomington 1830 Tazewell County John McLean (1791–1830), United States Representative and United States Senator from Illinois (the latter from 1824-25 and 1829-30) &&&&&&&&&0169572.&&&&&0169,572 &&&&&&&&&&&01184.&&&&&01,184 sq mi
(&&&&&&&&&&&03067.&&&&&03,067 km²)
State map highlighting McLean County
Menard County 129 Petersburg 1839 Sangamon County Pierre Menard (1766–1844), prominent early settler and first Lieutenant Governor of Illinois &&&&&&&&&&012705.&&&&&012,705 &&&&&&&&&&&&0314.&&&&&0314 sq mi
(&&&&&&&&&&&&0813.&&&&&0813 km²)
Mercer County 131 Aledo 1825 Schuyler County Hugh Mercer (1726-77), British officer in the Seven Years' War and general in the Continental Army during the American Revolutionary War &&&&&&&&&&016434.&&&&&016,434 &&&&&&&&&&&&0561.&&&&&0561 sq mi
(&&&&&&&&&&&01453.&&&&&01,453 km²)
State map highlighting Mercer County
Monroe County 133 Waterloo 1816 Randolph County and St. Clair County James Monroe (1758–1831), seventh United States Secretary of State, eighth United States Secretary of War, Governor of Virginia, and fifth President of the United States &&&&&&&&&&032957.&&&&&032,957 &&&&&&&&&&&&0388.&&&&&0388 sq mi
(&&&&&&&&&&&01005.&&&&&01,005 km²)
State map highlighting Monroe County
Montgomery County 135 Hillsboro 1821 Bond and Madison County Gen. Richard Montgomery (1738-75), brigadier-general in the Continental Army who led the unsuccessful invasion of Canada &&&&&&&&&&030104.&&&&&030,104 &&&&&&&&&&&&0704.&&&&&0704 sq mi
(&&&&&&&&&&&01823.&&&&&01,823 km²)
State map highlighting Montgomery County
Morgan County 137 Jacksonville 1823 Sangamon County Gen. Daniel Morgan (1736–1802), successful tactician in the American Revolutionary War and later United States Representative from Virginia &&&&&&&&&&035547.&&&&&035,547 &&&&&&&&&&&&0569.&&&&&0569 sq mi
(&&&&&&&&&&&01474.&&&&&01,474 km²)
State map highlighting Morgan County
Moultrie County 139 Sullivan 1843 Shelby and Macon County Gen. William Moultrie (1730–1805), American Revolutionary War general and Governor of South Carolina &&&&&&&&&&014846.&&&&&014,846 &&&&&&&&&&&&0336.&&&&&0336 sq mi
(&&&&&&&&&&&&0870.&&&&&0870 km²)
Ogle County 141 Oregon 1836 Jo Daviess Joseph Ogle (1737–1821), early settler in southwest Illinois, who helped found the first Methodist church in Illinois &&&&&&&&&&053497.&&&&&053,497 &&&&&&&&&&&&0759.&&&&&0759 sq mi
(&&&&&&&&&&&01966.&&&&&01,966 km²)
State map highlighting Ogle County
Peoria County 143 Peoria 1825 Fulton County The Peoria Native American tribe &&&&&&&&&0186494.&&&&&0186,494 &&&&&&&&&&&&0620.&&&&&0620 sq mi
(&&&&&&&&&&&01606.&&&&&01,606 km²)
State map highlighting Peoria County
Perry County 145 Pinckneyville 1827 Randolph and Jackson County Commodore Oliver Hazard Perry (1785–1819), American naval officer who led the victorious American forces at the Battle of Lake Erie &&&&&&&&&&022350.&&&&&022,350 &&&&&&&&&&&&0441.&&&&&0441 sq mi
(&&&&&&&&&&&01142.&&&&&01,142 km²)
Piatt County 147 Monticello 1841 DeWitt and Macon County John Piatt, the patriarch of a prominent settler family in the early history of the county &&&&&&&&&&016729.&&&&&016,729 &&&&&&&&&&&&0440.&&&&&0440 sq mi
(&&&&&&&&&&&01140.&&&&&01,140 km²)
Pike County 149 Pittsfield 1821 Madison, Bond, and Clark County Zebulon Pike (1779–1813), early explorer of the American Southwest, namesake of Pikes Peak &&&&&&&&&&016430.&&&&&016,430 &&&&&&&&&&&&0830.&&&&&0830 sq mi
(&&&&&&&&&&&02150.&&&&&02,150 km²)
State map highlighting Pike County
Pope County 151 Golconda 1816 Gallatin and Johnson County Nathaniel Pope (1784–1850), early Delegate from Illinois Territory to Congress and judge on the United States District Court for the District of Illinois &&&&&&&&&&&04470.&&&&&04,470 &&&&&&&&&&&&0371.&&&&&0371 sq mi
(&&&&&&&&&&&&0961.&&&&&0961 km²)
Pulaski County 153 Mound City 1843 Alexander and Johnson County Gen. Casimir Pulaski (1745-79), Polish American general of cavalry in the American Revolutionary War &&&&&&&&&&&06161.&&&&&06,161 &&&&&&&&&&&&0201.&&&&&0201 sq mi
(&&&&&&&&&&&&0521.&&&&&0521 km²)
Putnam County 155 Hennepin 1825 Fulton County Gen. Israel Putnam (1718-90), commander of American forces at the Battle of Bunker Hill &&&&&&&&&&&06006.&&&&&06,006 &&&&&&&&&&&&0160.&&&&&0160 sq mi
(&&&&&&&&&&&&0414.&&&&&0414 km²)
Randolph County 157 Chester 1795 St. Clair County Edmund Randolph (1753–1813), first Attorney General of the United States, and briefly United States Secretary of State &&&&&&&&&&033476.&&&&&033,476 &&&&&&&&&&&&0578.&&&&&0578 sq mi
(&&&&&&&&&&&01497.&&&&&01,497 km²)
State map highlighting Randolph County
Richland County 159 Olney 1841 Clay and Lawrence County Richland County, Ohio, itself named for its rich soil &&&&&&&&&&016233.&&&&&016,233 &&&&&&&&&&&&0360.&&&&&0360 sq mi
(&&&&&&&&&&&&0932.&&&&&0932 km²)
Rock Island County 161 Rock Island 1831 Jo Daviess County Rock Island &&&&&&&&&0147546.&&&&&0147,546 &&&&&&&&&&&&0427.&&&&&0427 sq mi
(&&&&&&&&&&&01106.&&&&&01,106 km²)
State map highlighting Rock Island County
Saline County 165 Harrisburg 1847 Gallatin County Salt springs within the county &&&&&&&&&&024913.&&&&&024,913 &&&&&&&&&&&&0383.&&&&&0383 sq mi
(&&&&&&&&&&&&0992.&&&&&0992 km²)
Sangamon County 167 Springfield 1821 Madison and Bond County Sangamon River &&&&&&&&&0197465.&&&&&0197,465 &&&&&&&&&&&&0868.&&&&&0868 sq mi
(&&&&&&&&&&&02248.&&&&&02,248 km²)
State map highlighting Sangamon County
Schuyler County 169 Rushville 1825 Pike and Fulton County Gen. Philip Schuyler (1733–1804), American Revolutionary War general and United States Senator from New York &&&&&&&&&&&07544.&&&&&07,544 &&&&&&&&&&&&0437.&&&&&0437 sq mi
(&&&&&&&&&&&01132.&&&&&01,132 km²)
Scott County 171 Winchester 1839 Morgan County Scott County, Kentucky, itself named after Charles Scott &&&&&&&&&&&05355.&&&&&05,355 &&&&&&&&&&&&0251.&&&&&0251 sq mi
(&&&&&&&&&&&&0650.&&&&&0650 km²)
Shelby County 173 Shelbyville 1827 Fayette County Isaac Shelby (1750–1826), soldier in the American Revolutionary War and War of 1812; first and fifth Governor of Kentucky &&&&&&&&&&022363.&&&&&022,363 &&&&&&&&&&&&0759.&&&&&0759 sq mi
(&&&&&&&&&&&01966.&&&&&01,966 km²)
St. Clair County 163 Belleville 1790 original two counties Arthur St. Clair (1737–1818), major general in the American Revolutionary War and first Governor of the Northwest Territory &&&&&&&&&0270056.&&&&&0270,056 &&&&&&&&&&&&0664.&&&&&0664 sq mi
(&&&&&&&&&&&01720.&&&&&01,720 km²)
State map highlighting St. Clair County
Stark County 175 Toulon 1839 Knox and Putnam County Gen. John Stark (1728–1822), general in the American Revolutionary War, called the "Hero of Bennington" &&&&&&&&&&&05994.&&&&&05,994 &&&&&&&&&&&&0288.&&&&&0288 sq mi
(&&&&&&&&&&&&0746.&&&&&0746 km²)
Stephenson County 177 Freeport 1837 Jo Daviess and Winnebago County Benjamin Stephenson (1769–1822), representative of Illinois Territory in the United States Congress from 1814 to 1816 &&&&&&&&&&047711.&&&&&047,711 &&&&&&&&&&&&0564.&&&&&0564 sq mi
(&&&&&&&&&&&01461.&&&&&01,461 km²)
State map highlighting Stephenson County
Tazewell County 179 Pekin 1827 Sangamon County Littleton Waller Tazewell (1774–1860), United States Senator from (and later governor of) Virginia &&&&&&&&&0135394.&&&&&0135,394 &&&&&&&&&&&&0649.&&&&&0649 sq mi
(&&&&&&&&&&&01681.&&&&&01,681 km²)
State map highlighting Tazewell County
Union County 181 Jonesboro 1818 Johnson County The federal union of the states &&&&&&&&&&017808.&&&&&017,808 &&&&&&&&&&&&0416.&&&&&0416 sq mi
(&&&&&&&&&&&01077.&&&&&01,077 km²)
State map highlighting Union County
Vermilion County 183 Danville 1826 Edgar County The Vermilion River &&&&&&&&&&081625.&&&&&081,625 &&&&&&&&&&&&0899.&&&&&0899 sq mi
(&&&&&&&&&&&02328.&&&&&02,328 km²)
State map highlighting Vermilion County
Wabash County 185 Mount Carmel 1824 Edwards County The Wabash River &&&&&&&&&&011947.&&&&&011,947 &&&&&&&&&&&&0224.&&&&&0224 sq mi
(&&&&&&&&&&&&0580.&&&&&0580 km²)
Warren County 187 Monmouth 1825 Schuyler County Joseph Warren (1741-75), played a role in American Patriot movements, a prominent early fatality in the American Revolutionary War &&&&&&&&&&017707.&&&&&017,707 &&&&&&&&&&&&0543.&&&&&0543 sq mi
(&&&&&&&&&&&01406.&&&&&01,406 km²)
State map highlighting Warren County
Washington County 189 Nashville 1818 St. Clair County George Washington (1732-99), commander-in-chief of American forces in the American Revolutionary War and first President of the United States &&&&&&&&&&014716.&&&&&014,716 &&&&&&&&&&&&0563.&&&&&0563 sq mi
(&&&&&&&&&&&01458.&&&&&01,458 km²)
Wayne County 191 Fairfield 1819 Edwards County Gen. "Mad" Anthony Wayne (1745-96), major general in the United States Army in the American Revolutionary War and the Northwest Indian War &&&&&&&&&&016760.&&&&&016,760 &&&&&&&&&&&&0714.&&&&&0714 sq mi
(&&&&&&&&&&&01849.&&&&&01,849 km²)
White County 193 Carmi 1815 Gallatin County Isaac White (1776–1811), resident of Illinois who enlisted in the Indiana militia and was killed at the Battle of Tippecanoe &&&&&&&&&&014665.&&&&&014,665 &&&&&&&&&&&&0495.&&&&&0495 sq mi
(&&&&&&&&&&&01282.&&&&&01,282 km²)
State map highlighting White County
Whiteside County 195 Morrison 1836 Jo Daviess and Henry County Samuel Whiteside (1783–1868), state legislator and militia leader &&&&&&&&&&058498.&&&&&058,498 &&&&&&&&&&&&0685.&&&&&0685 sq mi
(&&&&&&&&&&&01774.&&&&&01,774 km²)
State map highlighting Whiteside County
Will County 197 Joliet 1836 Cook and Iroquois County Conrad Will (1779–1835), physician, local businessman and longtime member of the state legislature &&&&&&&&&0677560.&&&&&0677,560 &&&&&&&&&&&&0837.&&&&&0837 sq mi
(&&&&&&&&&&&02168.&&&&&02,168 km²)
State map highlighting Will County
Williamson County 199 Marion 1839 Franklin County Hugh Williamson (1735–1819), delegate from North Carolina to the Philadelphia Convention &&&&&&&&&&066357.&&&&&066,357 &&&&&&&&&&&&0424.&&&&&0424 sq mi
(&&&&&&&&&&&01098.&&&&&01,098 km²)
Winnebago County 201 Rockford 1836 Jo Daviess Winnebago Native Americans &&&&&&&&&0295266.&&&&&0295,266 &&&&&&&&&&&&0514.&&&&&0514 sq mi
(&&&&&&&&&&&01331.&&&&&01,331 km²)
Woodford County 203 Eureka 1841 Tazewell and McLean County Gen. William Woodford (1734-80), brigadier general in the American Revolutionary War who died while a British prisoner &&&&&&&&&&038664.&&&&&038,664 &&&&&&&&&&&&0528.&&&&&0528 sq mi
(&&&&&&&&&&&01368.&&&&&01,368 km²)

Defunct counties

  • Dane County was renamed in 1840 to the current Christian County.
  • The original Knox County, Illinois, became extinct with the formation of the Illinois Territory in 1809 - or, more precisely, it became Knox County, Indiana. The modern Knox County, Illinois was formed much later and was not a part of the original Knox County.

List of counties in Illinois Facts for Kids. Kiddle Encyclopedia.