List of counties in Illinois

There are 102 counties in the state of Illinois.

Counties of Illinois

County	FIPS code	County seat	Established	Origin	Meaning of name	Population (2020)	Area	Map
Adams County	001	Quincy	1825	Pike County	John Quincy Adams (1767–1848), sixth President of the United States	65,737	855 sq mi (2,214 km2)
Alexander County	003	Cairo	1819	Union County	William M. Alexander, settler and state representative in the Illinois General Assembly	5,240	235 sq mi (609 km2)
Bond County	005	Greenville	1817	Crawford County, Edwards County, and Madison County	Shadrach Bond (1773–1832), first Governor of Illinois	16,725	380 sq mi (984 km2)
Boone County	007	Belvidere	1837	Winnebago County	Daniel Boone (1734–1820), trailblazer of the Wilderness Road in Kentucky	53,448	280 sq mi (725 km2)
Brown County	009	Mount Sterling	1839	Schuyler County	Jacob Brown (1775–1828), successful War of 1812 army officer responsible for Great Lakes defenses	6,244	305 sq mi (790 km2)
Bureau County	011	Princeton	1837	Putnam County	Pierre de Bureo, Frenchman, North American fur trader	33,244	869 sq mi (2,251 km2)
Calhoun County	013	Hardin	1825	Pike County	John C. Calhoun (1782–1850), South Carolina senator and seventh Vice President of the United States	4,437	253 sq mi (655 km2)
Carroll County	015	Mount Carroll	1839	Jo Daviess	Charles Carroll of Carrollton (1737–1832), signed the Declaration of Independence on behalf of Maryland	15,702	445 sq mi (1,153 km2)
Cass County	017	Virginia	1837	Morgan County	Lewis Cass (1782–1866), second governor of Michigan Territory, fourteenth United States Secretary of War	13,042	375 sq mi (971 km2)
Champaign County	019	Urbana	1833	Vermilion County	Champaign County, Ohio, which took its name from the French for "open level country"	205,865	996 sq mi (2,580 km2)
Christian County	021	Taylorville	1839	Sangamon County	Christian County, Kentucky, which was named after William Christian	34,032	709 sq mi (1,836 km2)
Clark County	023	Marshall	1819	Crawford County	George Rogers Clark (1752–1818), highest-ranking officer in the Northwest Territory during the American Revolution	15,455	501 sq mi (1,298 km2)
Clay County	025	Louisville	1824	Wayne, Lawrence, Fayette, and Crawford County	Henry Clay (1777–1852), Kentucky legislator who negotiated the Missouri Compromise	13,288	468 sq mi (1,212 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	36,899	474 sq mi (1,228 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	46,863	508 sq mi (1,316 km2)
Cook County	031	Chicago	1831	Putnam County	Daniel Pope Cook (1794–1827), politician and first Attorney General of Illinois	5,275,541	944 sq mi (2,445 km2)
Crawford County	033	Robinson	1816	Edwards County	William H. Crawford (1772–1834), ninth United States Secretary of War, seventh Secretary of the Treasury	18,679	443 sq mi (1,147 km2)
Cumberland County	035	Toledo	1843	Coles County	Disputed: Cumberland Road, which entered the county; Cumberland, Maryland; or Cumberland River in Kentucky	10,450	345 sq mi (894 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	100,420	631 sq mi (1,634 km2)
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	15,516	397 sq mi (1,028 km2)
Douglas County	041	Tuscola	1859	Coles County	Stephen A. Douglas (1813–1861), prominent Illinois Democrat who engaged in debates with Abraham Lincoln	19,740	416 sq mi (1,077 km2)
DuPage County	043	Wheaton	1839	Cook County	DuPage River	932,877	327 sq mi (847 km2)
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	16,866	623 sq mi (1,614 km2)
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	6,245	222 sq mi (575 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	34,668	478 sq mi (1,238 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.	21,488	716 sq mi (1,854 km2)
Ford County	053	Paxton	1859	Vermilion County	Thomas Ford (1800–1850), eighth Governor of Illinois; served during the Illinois Mormon War	13,534	485 sq mi (1,256 km2)
Franklin County	055	Benton	1818	White County and Gallatin County	Benjamin Franklin (1706–1790), prolific writer, inventor, and politician; key factor in the American Revolution	37,804	408 sq mi (1,057 km2)
Fulton County	057	Lewistown	1823	Pike County	Robert Fulton (1765–1815), inventor of the steamboat	33,609	865 sq mi (2,240 km2)
Gallatin County	059	Shawneetown	1812	Randolph County	Albert Gallatin (1761–1849), fourth and longest-serving United States Secretary of the Treasury	4,946	322 sq mi (834 km2)
Greene County	061	Carrollton	1821	Madison County	Nathanael Greene (1742–1786), major general in the Continental Army	11,985	543 sq mi (1,406 km2)
Grundy County	063	Morris	1841	LaSalle County	Felix Grundy (1777–1840), Tennessean senator who served as the thirteenth United States Attorney General	52,533	418 sq mi (1,083 km2)
Hamilton County	065	McLeansboro	1821	White County	Alexander Hamilton (1755–1804), first United States Secretary of the Treasury	7,993	434 sq mi (1,124 km2)
Hancock County	067	Carthage	1825	Adams County	John Hancock (1737–1793), first governor of the Massachusetts colony and president of the Second Continental Congress	17,620	793 sq mi (2,054 km2)
Hardin County	069	Elizabethtown	1839	Pope County	Hardin County, Kentucky, which was named after John Hardin	3,649	177 sq mi (458 km2)
Henderson County	071	Oquawka	1841	Warren County	Henderson County, Kentucky, which was itself named after Richard Henderson	6,387	378 sq mi (979 km2)
Henry County	073	Cambridge	1825	Fulton County	Patrick Henry (1736–1799), American Revolutionary War figure; first and sixth Governor of Virginia	49,284	822 sq mi (2,129 km2)
Iroquois County	075	Watseka	1833	Vermilion County	Iroquois Native Americans	27,077	1,117 sq mi (2,893 km2)
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	52,974	584 sq mi (1,513 km2)
Jasper County	079	Newton	1831	Clay and Crawford County	Sgt. William Jasper (c. 1750–1779), American Revolutionary War soldier popularized by Parson Weems	9,287	494 sq mi (1,279 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	37,113	571 sq mi (1,479 km2)
Jersey County	083	Jerseyville	1839	Greene County	State of New Jersey, from which many early settlers hailed	21,512	369 sq mi (956 km2)
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	22,035	600 sq mi (1,554 km2)
Johnson County	087	Vienna	1812	Randolph County	Richard Mentor Johnson (c. 1780–1850), ninth Vice President of the United States and United States Senator from Kentucky	13,308	343 sq mi (888 km2)
Kane County	089	Geneva	1836	LaSalle County	Elias Kane (1794–1835), United States Senator from Illinois	516,522	519 sq mi (1,344 km2)
Kankakee County	091	Kankakee	1853	Iroquois and Will County	Kankakee River	107,502	676 sq mi (1,751 km2)
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	131,869	320 sq mi (829 km2)
Knox County	095	Galesburg	1825	Fulton County	Gen. Henry Knox (1750–1806), American Revolutionary War general and first United States Secretary of War	49,967	716 sq mi (1,854 km2)
Lake County	097	Waukegan	1839	McHenry County	Lake Michigan	714,342	443 sq mi (1,147 km2)
LaSalle County	099	Ottawa	1831	Putnam and Tazewell County	Sieur de la Salle (1643–1687), French explorer of the Great Lakes	109,658	1,135 sq mi (2,940 km2)
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!"	15,280	372 sq mi (963 km2)
Lee County	103	Dixon	1839	Ogle County	"Light Horse" Henry Lee III (1756–1818), American Revolutionary War officer and ninth Governor of Virginia	34,145	724 sq mi (1,875 km2)
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	35,815	1,043 sq mi (2,701 km2)
Logan County	107	Lincoln	1839	Sangamon County	John Logan, country doctor and early settler, and the father of John A. Logan	27,987	618 sq mi (1,601 km2)
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	103,998	580 sq mi (1,502 km2)
Macoupin County	117	Carlinville	1829	Greene County	Native American word macoupin, meaning "American lotus"	44,967	862 sq mi (2,233 km2)
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	265,859	716 sq mi (1,854 km2)
Marion County	121	Salem	1823	Fayette and Jefferson County	Francis Marion (c. 1732–1795), general in the American Revolutionary War known as "The Swamp Fox"	37,729	572 sq mi (1,481 km2)
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	11,742	386 sq mi (1,000 km2)
Mason County	125	Havana	1841	Tazewell and Menard County	Named after Mason County, Kentucky, itself named after George Mason	13,086	539 sq mi (1,396 km2)
Massac County	127	Metropolis	1843	Pope and Johnson County	Fort Massac, a colonial-era fort on the Ohio River	14,169	237 sq mi (614 km2)
McDonough County	109	Macomb	1826	Schuyler County	Commodore Thomas Macdonough (1783–1825), commander of American naval forces at the Battle of Plattsburgh	27,238	589 sq mi (1,526 km2)
McHenry County	111	Woodstock	1836	Cook and LaSalle County	Major William McHenry (c. 1771–1835), officer during several campaigns against Native Americans and was a member of the Illinois legislature	310,229	603 sq mi (1,562 km2)
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)	170,954	1,183 sq mi (3,064 km2)
Menard County	129	Petersburg	1839	Sangamon County	Pierre Menard (1766–1844), prominent early settler and first Lieutenant Governor of Illinois	12,297	314 sq mi (813 km2)
Mercer County	131	Aledo	1825	Schuyler County	Hugh Mercer (1726–1777), British officer in the Seven Years' War and general in the Continental Army during the American Revolutionary War	15,699	561 sq mi (1,453 km2)
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	34,962	385 sq mi (997 km2)
Montgomery County	135	Hillsboro	1821	Bond and Madison County	Gen. Richard Montgomery (1738–1775), brigadier-general in the Continental Army who led the unsuccessful invasion of Canada	28,288	703 sq mi (1,821 km2)
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	32,915	568 sq mi (1,471 km2)
Moultrie County	139	Sullivan	1843	Shelby and Macon County	Gen. William Moultrie (1730–1805), American Revolutionary War general and Governor of South Carolina	14,526	335 sq mi (868 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	51,788	758 sq mi (1,963 km2)
Peoria County	143	Peoria	1825	Fulton County	The Peoria Native American tribe	181,830	618 sq mi (1,601 km2)
Perry County	145	Pinckneyville	1827	Randolph and Jackson County	Cmdre. Oliver Hazard Perry (1785–1819), American naval officer who led the victorious American forces at the Battle of Lake Erie	20,945	441 sq mi (1,142 km2)
Piatt County	147	Monticello	1841	DeWitt and Macon County	James A. Piatt, the patriarch of a prominent settler family in the early history of the county	16,673	439 sq mi (1,137 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	14,739	831 sq mi (2,152 km2)
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	3,763	368 sq mi (953 km2)
Pulaski County	153	Mound City	1843	Alexander and Johnson County	Gen. Casimir Pulaski (1745–1779), Polish American general of cavalry in the American Revolutionary War	5,193	199 sq mi (515 km2)
Putnam County	155	Hennepin	1825	Fulton County	Gen. Israel Putnam (1718–1790), commander of American forces at the Battle of Bunker Hill	5,637	160 sq mi (414 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	30,163	575 sq mi (1,489 km2)
Richland County	159	Olney	1841	Clay and Lawrence County	Richland County, Ohio, itself named for its rich soil	15,813	360 sq mi (932 km2)
Rock Island County	161	Rock Island	1831	Jo Daviess County	Rock Island	144,672	427 sq mi (1,106 km2)
Saline County	165	Harrisburg	1847	Gallatin County	The Saline River and salt springs in the county	23,768	379 sq mi (982 km2)
Sangamon County	167	Springfield	1821	Madison and Bond County	Sangamon River	196,343	868 sq mi (2,248 km2)
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	6,902	437 sq mi (1,132 km2)
Scott County	171	Winchester	1839	Morgan County	Scott County, Kentucky, itself named after Charles Scott	4,949	250 sq mi (647 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	20,990	758 sq mi (1,963 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	257,400	657 sq mi (1,702 km2)
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"	5,400	288 sq mi (746 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	44,630	564 sq mi (1,461 km2)
Tazewell County	179	Pekin	1827	Sangamon County	Littleton Waller Tazewell (1774–1860), United States Senator from (and later governor of) Virginia	131,343	646 sq mi (1,673 km2)
Union County	181	Jonesboro	1818	Johnson County	The union of the United States	17,244	413 sq mi (1,070 km2)
Vermilion County	183	Danville	1826	Edgar County	The Vermilion River	74,188	898 sq mi (2,326 km2)
Wabash County	185	Mount Carmel	1824	Edwards County	The Wabash River	11,361	223 sq mi (578 km2)
Warren County	187	Monmouth	1825	Schuyler County	Joseph Warren (1741–1775), played a role in American Patriot movements, a prominent early fatality in the American Revolutionary War	16,835	542 sq mi (1,404 km2)
Washington County	189	Nashville	1818	St. Clair County	George Washington (1732–1799), commander-in-chief of American forces in the American Revolutionary War and first President of the United States	13,761	562 sq mi (1,456 km2)
Wayne County	191	Fairfield	1819	Edwards County	Gen. "Mad" Anthony Wayne (1745–1796), major general in the United States Army in the American Revolutionary War and the Northwest Indian War	16,179	713 sq mi (1,847 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	13,877	494 sq mi (1,279 km2)
Whiteside County	195	Morrison	1836	Jo Daviess and Henry County	Samuel Whiteside (1783–1868), state legislator and militia leader	55,691	684 sq mi (1,772 km2)
Will County	197	Joliet	1836	Cook and Iroquois County	Conrad Will (1779–1835), physician, local businessman and longtime member of the state legislature	696,355	835 sq mi (2,163 km2)
Williamson County	199	Marion	1839	Franklin County	Williamson County, Tennessee, which was named for Hugh Williamson	67,153	420 sq mi (1,088 km2)
Winnebago County	201	Rockford	1836	Jo Daviess County	Winnebago Native Americans	285,350	513 sq mi (1,329 km2)
Woodford County	203	Eureka	1841	Tazewell and McLean County	Woodford County, Kentucky, which was named for William Woodford	38,467	527 sq mi (1,365 km2)

Old 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. It became Knox County, Indiana. The modern Knox County, Illinois was formed much later and was not a part of the original Knox County.