| Name of County
|
Date Formed
|
Boundary Changes
|
Parent County
|
Counties Created by Boundary Changes
|
| Adams
|
1797 Jul 10
|
Details
|
Hamilton
|
Brown 1817, Gallia 1803, Highland 1805, Pike 1815, Ross 1789, Scioto 1803
|
| Allen
|
1820 Feb 12
|
Details
|
Shelby
|
Auglaize 1848
|
| Ashland
|
1846 Feb 24
|
Details
|
Wayne, Richland, Huron, Lorain
|
none
|
| Ashtabula
|
1807 Feb 10
|
Details
|
Trumbull, Geauga
|
none
|
| Athens
|
1805 Feb 20
|
Details
|
Washington
|
Hocking 1818, jackson 1816, Meigs 1819, Vinton 1850
|
| Auglaize
|
1848 Feb 14
|
Details
|
Allen, Mercer
|
none
|
| Belmont
|
1801 Sep 07
|
Details
|
Jefferson, Washington
|
Guernsey 1810
|
| Brown
|
1817 Dec 27
|
Details
|
Adams, Clermont
|
none
|
| Butler
|
1803 Mar 24
|
Details
|
Hamilton
|
Preble 1808
|
| Carroll
|
1832 Dec 25
|
Details
|
Columbia, Stark, Harrison, Jefferson, Tuscarawas
|
none
|
| Champaign
|
1805 Feb 20
|
Details
|
Greene, Franklin
|
Clark 1817, Logan 1818
|
| Clark
|
1817 Dec 26
|
Details
|
Champaign, Madison, Greene
|
none
|
| Clermont
|
1800 Dec 06
|
Details
|
Hamilton
|
Brown 1817, Highland 1805
|
| Clinton
|
810 Feb 19
|
Details
|
Highland, Warren
|
none
|
| Columbiana
|
1803 Mar 25
|
Details
|
Jefferson, Washington
|
Carroll 1832, Mahoning 1846, Stark 1808, Wayne 1796
|
| Coshocton
|
1810 Jan 31
|
Details
|
Muskingum, Tuscarawas
|
Holmes 1824
|
| Crawford
|
1820 Feb 12
|
Details
|
Delaware
|
Wyandot 1845
|
| Cuyahoga
|
1808 Feb 10
|
Details
|
Geauga
|
Huron 1809, Lake 1840, Lorain 1822
|
| Darke
|
1809 Jan 03
|
Details
|
Miami
|
Mercer 1820, Paulding 1820, Van Wert 1820, Williams 1820
|
| Defiance
|
1845 Mar 04
|
Details
|
Williams, henry, Paulding
|
none
|
| Delaware
|
1808 Feb 10
|
Details
|
Franklin
|
Crawford 1820, Marion 1820, Morrow 1848, Union 1820
|
| Erie
|
1838 Mar 15
|
Details
|
Huron, Sandusky
|
Ottawa 1840
|
| Fairfield
|
1800 Dec 09
|
Details
|
Ross, Washington
|
Hocking 1818, Knox 1808, Licking 1808, Muskingum 1804, Perry 1817, Pickaway 1810, Richland 1808
|
| Fayette
|
1810 Feb 19
|
Details
|
Ross, Highland
|
none
|
| Franklin
|
1803 Mar 30
|
Details
|
Ross, Wayne
|
Champaign 1805, Delaware 1808, Madison 1810, Union 1820, Pickaway 1810
|
| Fulton
|
1850 Feb 28
|
Details
|
Lucas, Henry, Williams
|
none
|
| Gallia
|
1850 Feb 28
|
Details
|
Washington, Adams
|
Jackson 1816, Lawrence 1815, Meigs 1819, Vinton 1850
|
| Geauga
|
1805 Dec 31
|
Details
|
Trumbull
|
Ashtabula 1807, Cuayhoga 1808, Lake 1840
|
| Greene
|
1803 Mar 24
|
Details
|
Hamilton, Ross
|
Champaign 1805, Clark 1817
|
| Guernsey
|
1810 Jan 31
|
Details
|
Belmont, Muskingum
|
Monroe 1813, Morgan 1817, Noble 1851
|
| Hamilton
|
1790 Jan 02
|
Details
|
Northwest Territory
|
Adams 1797, Butler 1803, Clermont 1800, Greene, 1803, Warren 1803
|
| Hancock
|
1820 Feb 12
|
Details
|
Logan
|
Wyandot 1845
|
| Hardin
|
1820 Feb 12
|
Details
|
Logan
|
Wyandot 1845
|
| Harrison
|
1813 Jan 02
|
Details
|
Jefferson, Tuscarawas
|
Carroll 1832
|
| Henry
|
1820 Feb 12
|
Details
|
Shelby
|
Defiance 1845, Fulton 1850, Lucas 1835
|
| Highland
|
1805 Feb 18
|
Details
|
Ross, Adams, Clermont
|
Clinton 1810, Fayette 1810
|
| Hocking
|
1818 Jan 03
|
Details
|
Athens, Ross, Fairfield
|
Vinton 1850
|
| Holmes
|
1824 Jan 20
|
Details
|
Coshocton, Wayne, Tuscarawas
|
none
|
| Huron
|
1809 Feb 07
|
Details
|
Portage, Cuyahoga
|
Ashland 1846, Erie 1838, Lorain 1822, Seneca 1820, Sandusky 1820
|
| Jackson
|
1815 Jan 12
|
Details
|
Scioto, Galla, Athens, Ross
|
Vinton 1850
|
| Jefferson
|
1797 Jul 27
|
Details
|
Washington
|
Belmont 1801, Carroll 1832, Harrison 1813, Trumbull 1800, Columbiana 1803
|
| Knox
|
1808 Jan 30
|
Details
|
Fairfield
|
Morrow 1848
|
| Lake
|
1840 Mar 06
|
Details
|
Geauga, Cuyahoga
|
none
|
| Lawrence
|
1815 Dec 21
|
Details
|
Gallia, Scioto
|
none
|
| Licking
|
1808 Jan 30
|
Details
|
Fairifled
|
none
|
| Logan
|
1818 Dec 30
|
Details
|
Champaign
|
Hancock 1820, Hardin 1820, Union 1820, Wood 1820
|
| Lorain
|
1822 Dec 26
|
Details
|
Huron, Cuyahoga, Medina
|
Ashland 1846
|
| Lucas
|
1835 Jun 20
|
Details
|
Wood, Sandusky, Henry
|
Fulton 1850, Ottawa 1840
|
| Madison
|
1810 Feb 16
|
Details
|
Franklin
|
Clark 1817, Union 1820
|
| Mahoning
|
1846 Feb 16
|
Details
|
Columbiana, Trumbull
|
none
|
| Marion
|
1820 Feb 12
|
Details
|
Delaware
|
Morrow 1848, Wyandot 1845
|
| Medina
|
1812 Feb 18
|
Details
|
Portage
|
Lorain 1822, Summit 1840
|
| Meigs
|
1819 Jan 21
|
Details
|
Gallia, Athens
|
none
|
| Mercer
|
1820 Feb 12
|
Details
|
Darke
|
Auglaize 1848
|
| Miami
|
1807 Jan 16
|
Details
|
Montgomery
|
Darke 1809, Shelby 1819
|
| Monroe
|
1813 Jan 29
|
Details
|
Guernsey
|
Noble 1851
|
| Montgomery
|
1803 Mar 24
|
Details
|
Hamilton, Wayne
|
Miami 1807, Preble 1808
|
| Morgan
|
1817 Dec 29
|
Details
|
Washington, Guernsey, Muskingum
|
Noble 1851
|
| Morrow
|
1848 Feb 24
|
Details
|
Knox, Delaware, Marion, Richland
|
none
|
| Muskingum
|
1804 Jan 07
|
Details
|
Washington, Fairfield
|
Coshocton 1810, Guernsey 1810, Morgan 1817, Fairfield 1817, Tuscarawas 1808
|
| Noble
|
1851 Mar 11
|
Details
|
Monroe, Washington, Morgan, Guernsey
|
none
|
| Ottawa
|
1840 Mar 06
|
Details
|
Erie, Sandusky, Lucas
|
none
|
| Paulding
|
1820 Feb 12
|
Details
|
Drake
|
Defiance 1845
|
| Perry
|
1817 Dec 26
|
Details
|
Washington, Fairfield, Muskingum
|
none
|
| Pickaway
|
1810 Jan 12
|
Details
|
Ross, Fairfield, Franklin
|
none
|
| Pike
|
1815 Jan 04
|
Details
|
Ross, Adams, Scioto
|
none
|
| Portage
|
1807 Feb 10
|
Details
|
Trumbull
|
Huron 1809, Medina 1812, Summit 1840
|
| Preble
|
1808 Feb 15
|
Details
|
Montgomery, Butler
|
none
|
| Putnam
|
1820 Feb 12
|
Details
|
Shelby
|
none
|
| Richland
|
1808 Jan 30
|
Details
|
Fairfield
|
Ashland 1846, Morrow 1848
|
| Ross
|
1798 Aug 20
|
Details
|
Adams, Washington
|
Fairfield 1800, Fayette 1810, Pike 1815, Franklin 1803, Greene 1803, Highland 1805, Hocking 1818, Jackson 1816, Pickaway 1810, Vinton 1850
|
| Sandusky
|
1820 Feb 12
|
Details
|
Huron
|
Erie 1838, Lucas 1835, Ottawa 1840
|
| Scioto
|
1803 Mar 24
|
Details
|
Adams
|
Jackson 1816, Lawrence 1815, Pike 1815
|
| Seneca
|
1820 Feb 12
|
Details
|
Huron
|
none
|
| Shelby
|
1819 Jan 07
|
Details
|
Miami
|
Allen 1820, Henry 1820, Putnam 1820
|
| Stark
|
1808 Feb 13
|
Details
|
Columbiana
|
Carroll 1832, Summit 1840
|
| Summit
|
1840 Mar 03
|
Details
|
Portage, Medina, Stark
|
none
|
| Trumbull
|
1800 Jul 10
|
Details
|
Jefferson, Wayne
|
Ashtabula 1807, Geauga 1805, Portage 1807,Mahoning 1846
|
| Tuscarawas
|
1808 Feb 13
|
Details
|
Muskingum
|
Carroll 1832, Coshocton 1810, Holmes 1824, Harrison 1813
|
| Union
|
1820 Jan 10
|
Details
|
Franklin, Madison, Logan, Delaware
|
none
|
| Van Wert
|
1820 Feb 12
|
WERT Details
|
Drake
|
none
|
| Vinton
|
1850 Mar 23
|
Details
|
Gallia, Athens, Ross, Jackson, Hocking
|
none
|
| Warren
|
1803 Mar 24
|
Details
|
Hamilton
|
Clinton 1810
|
| Washington
|
1788 Jul 27
|
Details
|
Northwest Territory
|
Athens 1805, Belmont 1801, Columbiana 1803, Fairfield 1800, Gallia 1803, Jefferson 1797, Monroe 1813, Morgan 1817, Muskingum 1804, Nole 1851, Perry 1817, Ross 1798
|
| Wayne
|
1796 Aug 15
|
Details
|
Columbia
|
Ashland 1846, Holmes 1824
|
| Williams
|
1820 eb 2
|
Details
|
Drake
|
Defiance 1845, Fulton 1850
|
| Wood
|
1820 Feb 12
|
Details
|
Logan
|
Lucas 1835
|
| Wyandot
|
1845 Feb 03
|
Details
|
Marion, Crawford, Hardin, Hancock
|
none
|