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Ohio Geography
Formation of Counties Timeline
 
Year Event
1770 George Washington began surveying land west of Virginia, land that later became the Northwest Territory and which, later still, became the states of Ohio, Michigan, Indiana, Illinois, Wisconsin, and part of Minnesota.
1778 In Virginia, Illinois Co. was formed from Augusta Co., included land north and west of what would become West Virginia (i.e., what would become eastern and southeastern Ohio).
1785 Treaty of Harmar addressed issues with Amerindians.  Settlers began arriving in what would become the Northwest Territory.
1787 The Continental Congress created the Northwest Territory on 13 Jul 1787.
1788 First organized European settlement in the Northwest Territory at Marietta (Washington Co., OH).
Washington Co. formed as first  county in the Northwest Territory (included most of what would become eastern and southeastern Ohio).
1790 Hamilton, ["Old"] Knox, and St. Clair Cos. formed as original counties of the Northwest Territory.  Hamilton Co. encompassed what would become the southwestern corner of Ohio; ["Old"] Knox Co. encompassed what would become west-central and northwestern Ohio, the entire state of Indiana, western Michigan, and eastern Illinois and Wisconsin; St. Clair Co. encompassed southwestern Illinois.
1792 Hamilton Co. expanded to include all of what would become western Ohio, plus Michigan.
1796 ["Old"] Wayne Co. formed from northern Hamilton Co. and new area; included all of what would become northwestern and north-central Ohio and the state of Michigan.  Referred to here and in other tables as "Old" Wayne Co.
1797 Adams Co. formed from Hamilton and Washington Cos.; included much of what would become central and south-central Ohio.
Jefferson Co. formed from Washington Co.; included what would become the northeastern counties of Ohio.
1798 Ross Co.  was formed from Adams, Hamilton, and Washington Cos.
Hamilton Co. gained from ["Old"] Knox Co., which consequently ceased to exist in Ohio.
Adams Co. gained from Hamilton Co.
1799 Jefferson Co. gained from Washington Co.
1800 Indiana Territory created from Northwest Territory.  ["Old"] Knox, Randolph, and St. Clair Cos. became part of Indiana Territory.
1800 Connecticut relinquished its "Western Reserve" claims in northeastern Ohio.
Clermont Co. formed from Hamilton Co.
Fairfield Co. formed from Ross and Washington Cos.
Trumbull Co. formed from Jefferson and "Old" Wayne Cos.
1801 Belmont Co. formed from Jefferson and Washington Cos.
1803 Ohio becomes the first state formed from the Northwest Territory on 1 Mar 1803.
1803 Butler Co. formed from Hamilton Co.
Columbiana Co. formed from Jefferson Co.
Franklin Co. formed from Ross Co. and new area.
Gallia Co. formed from Washington Co.
Greene Co. formed from Hamilton and Ross Cos. and new area.
Montgomery Co. formed from Hamilton Co. and new area.
Scioto Co. formed from Adams Co.
Warren Co. formed from Hamilton Co.
"Old" Wayne Co. eliminated from Ohio.
1804 Muskingum Co. formed from Washington and Fairfield Cos.
Scioto Co. gained from Gallia Co.
1805 Michigan Territory formed from Northwest Territory
1805 Athens Co. formed from Washington Co.
Champaign Co. formed from Greene and Franklin Cos.
Highland Co. formed from Ross, Adams, and Clermont Cos.
1806 Geauga Co. formed from Trumbull Co.
1807 Miami Co. formed from Montgomery Co.
Athens Co. exchanged land with Gallia and Washington Cos.
Jefferson Co. gained new area.
1808 Ashtabula Co. formed from Trumbull and Geauga Cos.; unincorporated area attached to Ashtabula.
Cuyahoga Co. formed from Geauga Co.; unincorporated area attached to Cuyahoga.
Delaware Co. formed from Franklin Co.
Knox Co. formed from Fairfield and Franklin Cos.
Licking Co. formed from Fairfield Co.
Portage Co. formed from Trumbull Co.
Preble Co. formed from Montgomery and Butler Cos.
Richland Co. formed from Franklin Co. and unincorporated area.
Stark Co. formed from Columbiana and Muskingum Cos. and unincorporated area.
Tuscarawas Co. formed from Muskingum Co.
Wayne Co. formed from unincorporated area.
Butler Co. gained from Hamilton Co.
1809 Darke Co. formed from Miami Co.
Huron Co. formed from Geauga and Portage Cos.
Trumbull Co. gained from Ashtabula Co.
Tuscarawas Co. gained from Jefferson Co.
Stark Co. locally organized.
1810 Federal Census the Ohio census was lost, except for Washington Co.
1810 Clinton Co. formed from Highland and Warren Cos.
Coshocton Co. formed from Muskingum and Tuscarawas Cos.
Fayette Co. formed from Ross and Highland Cos.
Guernsey Co. formed from Belmont and Muskingum Cos.
Madison Co. formed from Franklin Co.
Pickaway Co. formed from Ross, Fairfield, and Franklin Cos.
Cuyahoga Co. gained from Geauga Co.
Cuyahoga Co. locally organized.
1811 Ashtabula Co. gained from Trumbull Co.
Huron Co. gained from Cuyahoga Co.
Portage Co. lost to non-county area.
Ashtabula and Coshocton Cos. locally organized
1812 Medina Co. formed from non-county area that was formerly part of Portage Co.
Darke Co. gained from Montgomery Co.
Miami Co. gained from Montgomery Co.
Huron Co. gained from Cuyahoga Co.
Wayne Co. locally organized.
1813 Harrison Co. formed from Jefferson and Tuscarawas Cos.
Monroe Co. formed from Belmont, Washington, and Guernsey Cos.
Clinton Co. gained from Highland Co.
Richland Co. locally organized.
1814 Athens Co. exchanged land with Washington Co.
1815 Lawrence Co. formed from Gallia and Scioto Cos.
Pike Co. formed from Ross, Scioto, and Adams Cos.
Clinton Co. gained from Highland and Warren Cos.
Monroe Co. gained from Washington Co.
Warren Co. gained from Butler Co.
Huran and Monroe Cos. locally organized.
1816 Jackson Co. formed from Scioto, Gallia, Athens, and Ross Cos.
1817 Morgan Co. formed from Washington, Guernsey, and Muskingum Cos.
Franklin Co. gained from Licking Co.
Lawrence Co. gained from Scioto Co.
Lawrence and Drake Cos. locally organized.
1818 Boundary dispute with Michigan Territory begins.
Brown Co. formed from Adams and Clermont Cos.
Clark Co. formed from Champaign, Madison, and Greene Cos.
Hocking Co. formed from Athens, Ross, and Fairfield Cos.
Logan Co. formed from Champaign Co.
Perry Co. formed from Washington, Fairfield, and Muskingum Cos.
Lawrence Co. gained from Gallia Co.
Scioto Co. gained from Lawrence Co.
Medina Co. locally organized.
1819 Meigs Co. formed from Gallia and Athens Cos.
Shelby Co. formed from Miami Co.
Monroe Co. gained from Morgan Co.
Morgan Co. locally organized.
1820 Hardin Co. formed from Delaware and Logan Cos.
Mercer Co. formed from Darke and Shelby Cos.
Sandusky Co. formed from Huron Co.
Union Co. formed from Delaware, Franklin, Logan, and Madison Cos.
1820 Federal Census
1820 Allen Co. formed from Shelby and Logan Cos.
Crawford Co. formed from Delaware Co.
Hancock Co. formed from Delaware and Logan Cos.
Henry Co. formed from Shelby and Logan Cos.
Marion Co. formed from Delaware Co.
Paulding Co. formed from Darke and Shelby Cos.
Putnam Co. formed from Shelby and Logan Cos.
Seneca Co. formed from Huron Co.
Van Wert Co. formed from Darke and Shelby Cos.
Williams Co. formed from Darke and Shelby Cos.
Wood Co. formed from Logan Co.
Madison Co. gained from Franklin Co.
1822 Lorain Co. formed from Huron, Cuyahoga, and Medina Cos.
1824 Holmes Co. formed from Coshocton, Wayne, and Tuscarawas Cos.
Lorain Co. locally organized.
Marion Co. locally organized.
Mercer Co. locally organized (was enumerated in 1820 census).
Seneca Co. locally organized.
Williams Co. locally organized.
1825 Holmes Co. locally organized.
1826 Mercer Co. gained from Shelby Co.
Scioto Co. gained from Lawrence Co.
Crawford Co. locally organized.
1827 Clark Co. exchanged land with Madison Co.
Cuyahoga Co. gained from Lorain Co.
Lorain Co. gained from Medina Co.
Portage Co. gained from Medina Co.
1828 Hancock Co. locally organized.
1830 Federal Census
1831 Allen Co. locally organized (was enumerated in the 1830 census)
1833 Carroll Co. formed from Columbiana, Stark, Harrison, Jefferson, and Tuscarawas Cos.
Hardin Co. locally organized (was enumerated in 1830 census).
1834 Ross Co. gained from Hocking Co.
Stark Co. gained from Carroll Co.
Henry Co. locally organized (was enumerated in 1830 census).
Putnam Co. locally organized (was enumerated in 1830 census).
1835 Boundary dispute with Michigan continues:  the "Toledo War."
Lucas Co. formed from Wood and Sandusky Cos.
1836 Boundary dispute with Michigan settled.
Lucas Co. gained from Henry and Wood Cos.
1837 Perry Co. gained from Licking Co.
Van Wert Co. locally organized.
1838 Erie Co. created from Huron and Sandusky Cos.
1839 Ross Co. gained from Lawrence Co.
Gallia Co. gained from Lawrence Co.
Paulding Co. locally organized.
1840 Lake Co. formed from Geauga and Cuyahoga Cos.
Ottawa Co. formed from Erie, Sandusky, and Lucas Cos.
Summit Co. formed from Portage, Medina, and Stark Cos.
1840 Federal Census
1841 Cuyahoga Co. gained from Geauga Co.
1843 Jackson Co. exchanged land with Pike Co.
1845 Defiance Co. formed from Williams, Henry, and Paulding Cos.
Wyandot Co. formed from Marion, Crawford, Hardin, and Lorain Cos.
Erie Co. gained from Ottawa Co.
Hocking Co. gained from Athens Co.
Madison Co. gained from Franklin Co.
Morgan Co. gained from Athens and Washington Cos.
1846 Ashland Co. formed from Wayne, Richland, Huron, and Lorain Cos.
Mahoning Co. formed from Columbiana and Trumbull Cos.
Morgan Co. gained from Washington Co.
1847 Richland Co. gained from Ashland Co.
1848 Auglaize Co. formed from Allen, Mercer, Darke, Hardin, Logan, Shelby, and Van Wert Cos.
Morrow Co. formed from Knox, Marion, Delaware, and Richland Cos.
Allen Co. gained from Putnam Co.
Putnam Co. gained from Van Wert Co.
Tuscarawas Co. gained from Stark Co.
1849 Richland Co. gained from Morrow Co.
1850 Fulton Co. formed from Lucas, Henry, and Williams Cos.
Vinton Co. formed from Gallia, Athens, Ross, Jackson, and Hocking Cos.
Hocking Co. gained from Fairfield Co.
1850 Federal Census
1851 Noble Co. formed from Monroe, Washington, Morgan, and Guernsey Cos.
Franklin Co. gained from Fairfield Co.
1860 Federal Census
1870 Federal Census
1874 Highland Co. gained from Brown Co.
1880 Federal Census
1883 Logan Co. exchanged land with Shelby Co.
1888 Logan Co. gained from Auglaize Co., which was the last change in Ohio county boundaries.
   
Source:  AniMap Plus: County Boundary Historical Atlas: with "SiteFinder," U.S. Place Name Database and U.S. Cemetery Database. (On CD.) Gold Bug Software, Alamo, CA.

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