Adams County	001	West Union	July 10, 1797	Hamilton County	John Adams (1735.1826), President of the United States when the county was organized	28,550	583.91 sq mi
(1,512 km2)	State map highlighting Adams County
Allen County	003	Lima	March 1, 1820	Shelby County	John Allen (1771/2-1813), a War of 1812 colonel[14]	106,331	404.43 sq mi
(1,047 km2)	State map highlighting Allen County
Ashland County	005	Ashland	February 24, 1846	Wayne, Richland, Huron, and Lorain Counties	Ashland, home of U.S. Senator from Kentucky Henry Clay.	53,139	424.37 sq mi
(1,099 km2)	State map highlighting Ashland County
Ashtabula County	007	Jefferson	June 7, 1807	Trumbull and Geauga Counties	Ashtabula River, which means "fish river" in an Algonquian language[15]	101,497	702.44 sq mi
(1,819 km2)	State map highlighting Ashtabula County
Athens County	009	Athens	March 1, 1805	Washington County	Athens in Greece	64,757	506.76 sq mi
(1,313 km2)	State map highlighting Athens County
Auglaize County	011	Wapakoneta	February 14, 1848	Allen, Mercer, Darke, Hardin, Logan, Shelby, and Van Wert Counties	Auglaize River, which means "fallen timbers river" in the Shawnee Indian language	45,949	401.25 sq mi
(1,039 km2)	State map highlighting Auglaize County
Belmont County	013	St. Clairsville	September 7, 1801	Jefferson and Washington Counties	Belle monte, which means "beautiful mountain" in French	70,400	537.35 sq mi
(1,392 km2)	State map highlighting Belmont County
Brown County	015	Georgetown	March 1, 1818	Adams and Clermont Counties	General Jacob Brown (1775.1828), an officer of the War of 1812	44,846	491.76 sq mi
(1,274 km2)	State map highlighting Brown County
Butler County	017	Hamilton	May 1, 1803	Hamilton County	General Richard Butler (1743.1791), killed at the Battle of the Wabash	368,130	467.27 sq mi
(1,210 km2)	State map highlighting Butler County
Carroll County	019	Carrollton	January 1, 1833	Columbiana, Stark, Harrison, Jefferson, and Tuscarawas Counties	Charles Carroll (1737.1832), last surviving signer of the United States Declaration of Independence	28,836	394.67 sq mi
(1,022 km2)	State map highlighting Carroll County
Champaign County	021	Urbana	March 1, 1805	Greene and Franklin Counties	French for "a plain", describing the land in the area	40,097	428.56 sq mi
(1,110 km2)	State map highlighting Champaign County
Clark County	023	Springfield	March 1, 1818	Champaign, Madison, and Greene Counties	General George Rogers Clark (1752.1818), defeated the Shawnee Indians in a battle near the Springfield area	138,333	399.86 sq mi
(1,036 km2)	State map highlighting Clark County
Clermont County	025	Batavia	December 6, 1800	Hamilton County	French for "clear mountain"	197,363	451.99 sq mi
(1,171 km2)	State map highlighting Clermont County
Clinton County	027	Wilmington	March 1, 1810	Highland and Warren Counties	George Clinton (1739.1812), vice-president when the county was organized	42,040	410.88 sq mi
(1,064 km2)	State map highlighting Clinton County
Columbiana County	029	Lisbon	May 1, 1803	Jefferson and Washington Counties	Derived from the words Christopher Columbus, European explorer of the Americas	107,841	532.46 sq mi
(1,379 km2)	State map highlighting Columbiana County
Coshocton County	031	Coshocton	January 31, 1810	Muskingum and Tuscarawas Counties	Delaware Indian word meaning "union of waters"	36,901	564.07 sq mi
(1,461 km2)	State map highlighting Coshocton County
Crawford County	033	Bucyrus	April 1, 1820	Delaware County	Colonel William Crawford (1732.1782), Revolutionary War officer	43,784	402.11 sq mi
(1,041 km2)	State map highlighting Crawford County
Cuyahoga County	035	Cleveland	June 7, 1807	Geauga County	Cuyahoga River, which means "crooked river" in an Iroquoian language[16]	1,249,352	458.49 sq mi
(1,187 km2)	State map highlighting Cuyahoga County
Darke County	037	Greenville	January 3, 1809	Miami County	General William Darke (1736.1801), Revolutionary War officer	52,959	599.80 sq mi
(1,553 km2)	State map highlighting Darke County
Defiance County	039	Defiance	April 7, 1845	Williams, Henry, and Paulding Counties	Fort Defiance, built in 1794 by General Anthony Wayne	39,037	411.16 sq mi
(1,065 km2)	State map highlighting Defiance County
Delaware County	041	Delaware	April 1, 1808	Franklin County	Delaware Indians	174,214	442.41 sq mi
(1,146 km2)	State map highlighting Delaware County
Erie County	043	Sandusky	March 15, 1838	Huron and Sandusky Counties	Erie Indians	77,079	254.88 sq mi
(660 km2)	State map highlighting Erie County
Fairfield County	045	Lancaster	December 9, 1800	Ross and Washington Counties	Named for the beauty of its "fair fields"	146,156	505.11 sq mi
(1,308 km2)	State map highlighting Fairfield County
Fayette County	047	Washington Court House	March 1, 1810	Ross and Highland Counties	Gilbert du Motier, marquis de La Fayette, French military officer and aristocrat who participated in both the American and French revolutions.	29,030	406.58 sq mi
(1,053 km2)	State map highlighting Fayette County
Franklin County	049	Columbus	April 30, 1803	Ross and Wayne Counties	Benjamin Franklin (1706.1791), Founding Father, author, printer, political theorist, scientist, inventor, and statesman	1,264,518	539.87 sq mi
(1,398 km2)	State map highlighting Franklin County
Fulton County	051	Wauseon	April 1, 1850	Lucas, Henry, and Williams Counties	Robert Fulton (1765.1815), inventor of the steamboat	42,698	406.78 sq mi
(1,054 km2)	State map highlighting Fulton County
Gallia County	053	Gallipolis	April 30, 1803	Washington and Adams Counties	Gaul, the ancient name of France	30,934	468.78 sq mi
(1,214 km2)	State map highlighting Gallia County
Geauga County	055	Chardon	March 1, 1806	Trumbull County	An Indian word meaning "raccoon"	93,389	403.66 sq mi
(1,045 km2)	State map highlighting Geauga County
Greene County	057	Xenia	May 1, 1803	Hamilton and Ross Counties	General Nathanael Greene (1742.1786), Revolutionary War officer	161,573	414.88 sq mi
(1,075 km2)	State map highlighting Greene County
Guernsey County	059	Cambridge	March 1, 1810	Belmont and Muskingum Counties	Island of Guernsey, from where most of the settlers originated	40,087	521.90 sq mi
(1,352 km2)	State map highlighting Guernsey County
Hamilton County	061	Cincinnati	January 2, 1790	One of the original counties	Alexander Hamilton (1755/7-1804), Secretary of the Treasury when the county was organized	802,374	407.36 sq mi
(1,055 km2)	State map highlighting Hamilton County
Hancock County	063	Findlay	April 1, 1820	Logan County	John Hancock (1737.1793), president of the Continental Congress	74,782	531.35 sq mi
(1,376 km2)	State map highlighting Hancock County
Hardin County	065	Kenton	April 1, 1820	Logan County	General John Hardin (1753.1792), Revolutionary War officer	32,058	470.29 sq mi
(1,218 km2)	State map highlighting Hardin County
Harrison County	067	Cadiz	February 1, 1813	Jefferson and Tuscarawas Counties	General William Henry Harrison (1773.1841), an officer of the War of 1812 and future President of the United States	15,864	403.53 sq mi
(1,045 km2)	State map highlighting Harrison County
Henry County	069	Napoleon	April 1, 1820	Shelby County	Patrick Henry (1736.1799), Revolutionary War-era legislator, orator, and scholar	28,215	416.50 sq mi
(1,079 km2)	State map highlighting Henry County
Highland County	071	Hillsboro	May 1, 1805	Ross, Adams, and Clermont Counties	Descriptive of the county's terrain	43,589	553.28 sq mi
(1,433 km2)	State map highlighting Highland County
Hocking County	073	Logan	March 1, 1818	Athens, Ross, and Fairfield Counties	Possibly derived from the Delaware Indian word "Hoch-Hoch-ing", meaning "bottle"	29,380	422.75 sq mi
(1,095 km2)	State map highlighting Hocking County
Holmes County	075	Millersburg	January 20, 1824	Coshocton, Wayne, and Tuscarawas Counties	Major Andrew Holmes (died 1814), a War of 1812 officer	42,366	422.99 sq mi
(1,096 km2)	State map highlighting Holmes County
Huron County	077	Norwalk	March 7, 1809	Portage and Cuyahoga Counties	Huron Indians	59,626	492.69 sq mi
(1,276 km2)	State map highlighting Huron County
Jackson County	079	Jackson	March 1, 1816	Scioto, Gallia, Athens, and Ross Counties	General Andrew Jackson (1767.1845), future President of the United States	33,225	420.28 sq mi
(1,089 km2)	State map highlighting Jackson County
Jefferson County	081	Steubenville	July 29, 1797	Washington County	Thomas Jefferson (1743.1826), Vice President when the county was organized, future President of the United States, and principal author of the Declaration of Independence	69,709	409.61 sq mi
(1,061 km2)	State map highlighting Jefferson County
Knox County	083	Mount Vernon	March 1, 1808	Fairfield County	General Henry Knox, the first Secretary of War	60,921	527.12 sq mi
(1,365 km2)	State map highlighting Knox County
Lake County	085	Painesville	March 6, 1840	Geauga and Cuyahoga Counties	Its location on Lake Erie	230,041	228.21 sq mi
(591 km2)	State map highlighting Lake County
Lawrence County	087	Ironton	December 21, 1815	Gallia and Scioto Counties	Captain James Lawrence (1781.1813), naval hero in the War of 1812	62,450	454.96 sq mi
(1,178 km2)	State map highlighting Lawrence County
Licking County	089	Newark	March 1, 1808	Fairfield County	Named for the salt licks in the area	166,492	686.50 sq mi
(1,778 km2)	State map highlighting Licking County
Logan County	091	Bellefontaine	March 1, 1818	Champaign County	General Benjamin Logan (c. 1742 . 1802), who destroyed Shawnee Indian towns in the county	45,858	458.44 sq mi
(1,187 km2)	State map highlighting Logan County
Lorain County	093	Elyria	December 26, 1822	Huron, Cuyahoga, and Medina Counties	Province of Lorraine, France	301,356	492.50 sq mi
(1,276 km2)	State map highlighting Lorain County
Lucas County	095	Toledo	June 20, 1835	Wood, Sandusky, and Huron Counties	Robert Lucas (1781.1853), Governor of Ohio when the county was created	441,815	340.46 sq mi
(882 km2)	State map highlighting Lucas County
Madison County	097	London	March 1, 1810	Franklin County	James Madison (1751.1836), fourth President of the United States	43,435	465.44 sq mi
(1,205 km2)	State map highlighting Madison County
Mahoning County	099	Youngstown	March 1, 1846	Columbiana and Trumbull Counties	Mahoning River, from an Indian word meaning "at the licks"	238,823	415.25 sq mi
(1,075 km2)	State map highlighting Mahoning County
Marion County	101	Marion	April 1, 1820	Delaware County	General Francis Marion (1732.1795), lieutenant colonel in the Continental Army and later brigadier general in the American Revolutionary War.	66,501	403.84 sq mi
(1,046 km2)	State map highlighting Marion County
Medina County	103	Medina	February 18, 1812	Portage County	Medina, world-renowned religious site in western Saudi Arabia	176,395	423 sq mi
(1,096 km2)	State map highlighting Medina County
Meigs County	105	Pomeroy	April 1, 1819	Gallia and Athens Counties	Return Jonathan Meigs, Jr. (1764.1825), Governor of Ohio and Postmaster General at the time the county was organized	23,770	429.42 sq mi
(1,112 km2)	State map highlighting Meigs County
Mercer County	107	Celina	April 1, 1820	Darke County	General Hugh Mercer (1726.1777), a Revolutionary War officer	40,814	463.27 sq mi
(1,200 km2)	State map highlighting Mercer County
Miami County	109	Troy	March 1, 1807	Montgomery County	Miami Indians	102,506	407.04 sq mi
(1,054 km2)	State map highlighting Miami County
Monroe County	111	Woodsfield	January 29, 1813	Belmont, Washington, and Guernsey Counties	James Monroe (1758.1831), Secretary of State when the county was organized and future President of the United States	14,642	455.54 sq mi
(1,180 km2)	State map highlighting Monroe County
Montgomery County	113	Dayton	May 1, 1803	Hamilton and Wayne Counties	General Richard Montgomery (1738.1775), a Revolutionary War officer	535,153	461.68 sq mi
(1,196 km2)	State map highlighting Montgomery County
Morgan County	115	McConnelsville	December 29, 1817	Washington, Guernsey, and Muskingum Counties	General Daniel Morgan (c. 1735 . 1802), a Revolutionary War officer	15,054	417.66 sq mi
(1,082 km2)	State map highlighting Morgan County
Morrow County	117	Mount Gilead	March 1, 1848	Knox, Marion, Delaware, and Richland Counties	Jeremiah Morrow (1771.1852), Governor of Ohio	34,827	406.22 sq mi
(1,052 km2)	State map highlighting Morrow County
Muskingum County	119	Zanesville	March 1, 1804	Washington and Fairfield Counties	An Indian word meaning "A town by the river" or "by the river side"	86,074	664.63 sq mi
(1,721 km2)	State map highlighting Muskingum County
Noble County	121	Caldwell	April 1, 1851	Monroe, Washington, Morgan, and Guernsey Counties	James Noble (1785.1831), an early settler and future U.S. Senator from Indiana	14,645	399.00 sq mi
(1,033 km2)	State map highlighting Noble County
Ottawa County	123	Port Clinton	March 6, 1840	Erie, Sandusky, and Lucas Counties	Named for the Ottawa Indians; Ottawa means "trader" in their language	41,428	254.95 sq mi
(660 km2)	State map highlighting Ottawa County
Paulding County	125	Paulding	April 1, 1820	Darke County	John Paulding (1758.1818), captor of spy John Andréuring the Revolutionary War	19,614	416.26 sq mi
(1,078 km2)	State map highlighting Paulding County
Perry County	127	New Lexington	March 1, 1818	Washington, Fairfield, and Muskingum Counties	Commodore Oliver Hazard Perry (1785.1819), a naval officer of the War of 1812	36,058	409.78 sq mi
(1,061 km2)	State map highlighting Perry County
Pickaway County	129	Circleville	March 1, 1810	Ross, Fairfield, and Franklin Counties	A misspelling of the Piqua tribe, a branch of the Shawnee	55,698	501.91 sq mi
(1,300 km2)	State map highlighting Pickaway County
Pike County	131	Waverly	February 1, 1815	Ross, Scioto, and Adams Counties	General Zebulon M. Pike (1779.1813), a War of 1812 officer and discoverer of Pikes Peak in Colorado in 1806	28,709	441.49 sq mi
(1,143 km2)	State map highlighting Pike County
Portage County	133	Ravenna	June 7, 1807	Trumbull County	Derived from an Indian portage	161,419	492.39 sq mi
(1,275 km2)	State map highlighting Portage County
Preble County	135	Eaton	March 1, 1808	Montgomery and Butler Counties	Captain Edward Preble (1761.1807), a Naval commander in the Revolutionary War	42,270	424.80 sq mi
(1,100 km2)	State map highlighting Preble County
Putnam County	137	Ottawa	April 1, 1820	Shelby County	General Israel Putnam (1718.1790), a Revolutionary War officer	34,499	483.87 sq mi
(1,253 km2)	State map highlighting Putnam County
Richland County	139	Mansfield	March 1, 1808	Fairfield County	Descriptive of the soil in the area	124,475	496.88 sq mi
(1,287 km2)	State map highlighting Richland County
Ross County	141	Chillicothe	August 20, 1798	Adams and Washington Counties	Named for U.S. Senator from Pennsylvania James Ross by territorial governor Arthur St. Clair	78,064	688.41 sq mi
(1,783 km2)	State map highlighting Ross County
Sandusky County	143	Fremont	April 1, 1820	Huron County	An Iroquois word meaning "cold water"	60,944	409.18 sq mi
(1,060 km2)	State map highlighting Sandusky County
Scioto County	145	Portsmouth	May 1, 1803	Adams County	Scioto River; Scioto is a Wyandot Indian word meaning "deer"	79,499	612.27 sq mi
(1,586 km2)	State map highlighting Scioto County
Seneca County	147	Tiffin	April 1, 1820	Huron County	Seneca Indians, who had a reservation in the county area at the time	56,745	550.59 sq mi
(1,426 km2)	State map highlighting Seneca County
Shelby County	149	Sidney	April 1, 1819	Miami County	General Isaac Shelby (1750.1826), a Revolutionary War officer and Governor of Kentucky,	49,423	409.27 sq mi
(1,060 km2)	State map highlighting Shelby County
Stark County	151	Canton	February 13, 1808	Columbiana County	General John Stark (1728.1822), a Revolutionary War officer; known as the "Hero of Bennington" for his exemplary service at the Battle of Bennington in 1777	375,586	576.14 sq mi
(1,492 km2)	State map highlighting Stark County
Summit County	153	Akron	March 3, 1840	Medina, Portage, and Stark Counties	Its location at the highest elevation along the Ohio and Erie Canal	541,781	419.38 sq mi
(1,086 km2)	State map highlighting Summit County
Trumbull County	155	Warren	July 10, 1800	Jefferson and Wayne Counties	Jonathan Trumbull (1710.1785), Governor of Connecticut when the county was organized	210,312	616.48 sq mi
(1,597 km2)	State map highlighting Trumbull County
Tuscarawas County	157	New Philadelphia	March 15, 1808	Muskingum County	Tuscarawas River, meaning "open mouth river"
or
the Tuscarawas tribe who lived on the river	92,582	567.58 sq mi
(1,470 km2)	State map highlighting Tuscarawas County
Union County	159	Marysville	April 1, 1820	Delaware, Franklin, Logan, and Madison Counties	Its formation by a union of four counties	52,300	436.65 sq mi
(1,131 km2)	State map highlighting Union County
Van Wert County	161	Van Wert	April 1, 1820	Darke County	Isaac Van Wart (1760.1828), captor of spy John Andréuring the Revolutionary War	28,744	410.09 sq mi
(1,062 km2)	State map highlighting Van Wert County
Vinton County	163	McArthur	March 23, 1850	Athens, Gallia, Hocking, Jackson, and Ross Counties	Samuel Finley Vinton (1792.1862), Ohio Statesman and U.S. Congressman	13,435	414.08 sq mi
(1,072 km2)	State map highlighting Vinton County
Warren County	165	Lebanon	May 1, 1803	Hamilton County	General Joseph Warren (1741.1775), a Revolutionary War officer	212,693	399.63 sq mi
(1,035 km2)	State map highlighting Warren County
Washington County	167	Marietta	July 27, 1788	One of the original counties	George Washington (1732.1799), commander of the Continental Army, president of the Constitutional Convention, and future President of the United States	61,778	635.15 sq mi
(1,645 km2)	State map highlighting Washington County
Wayne County	169	Wooster	March 1, 1808	From non-county area	General Anthony Wayne (1745.1796), a Revolutionary War officer	114,520	555.36 sq mi
(1,438 km2)	State map highlighting Wayne County
Williams County	171	Bryan	April 1, 1820	Darke County	David Williams (1754.1831), captor of spy John Andréuring the Revolutionary War	37,642	421.74 sq mi
(1,092 km2)	State map highlighting Williams County
Wood County	173	Bowling Green	April 1, 1820	Refactored from non-county territory	Eleazer D. Wood (1783.1814), founder of Fort Meigs	125,488	617.32 sq mi
(1,599 km2)	State map highlighting Wood County
Wyandot County	175	Upper Sandusky	February 3, 1845	Marion, Crawford, and Hardin Counties	Wyandot Indians	22,615	405.61 sq mi
(1,051 km2)	State map highlighting Wyandot County