Ohio Counties
| County | Date Founded | Parent County |
| Adams | 10 Jul 1797 | Hamilton |
| Allen | 12 Feb 1820 | Shelby |
| Ashland | 24 Feb 1846 | Wayne, Richland, Huron, Lorain |
| Ashtabula | 10 Feb 1807 | Trumbull, Geauga |
| Athens | 20 Feb 1805 | Washington |
| Auglaize | 14 Feb 1848 | Allen, Mercer, Darke, Hardin, Logan, Shelby, Van Wert |
| Belmont | 7 Sep 1801 | Jefferson, Washington |
| Brown | 27 Dec 1817 | Adams, Clermont |
| Butler | 24 Mar 1803 | Hamilton |
| Carroll | 25 Dec 1832 | Columbiana, Stark, Harrison, Jefferson, Tuscarawas |
| Champaign | 20 Feb 1805 | Greene, Franklin |
| Clark | 26 Dec 1817 | Champaign, Madison, Greene |
| Clermont | 6 Dec 1800 | Hamilton |
| Clinton | 19 Feb 1810 | Highland, Warren |
| Columbiana | 25 Mar 1803 | Jefferson, Washington |
| Coshocton | 31 Jan 1810 | Tuscarawas, Muskingum |
| Crawford | 12 Feb 1820 | Delaware |
| Cuyahoga | 10 Feb 1808 | Geauga |
| Darke | 3 Jan 1809 | Miami |
| Defiance | 4 Mar 1845 | Williams, Henry, Paulding |
| Delaware | 10 Feb 1808 | Franklin |
| Erie | 15 Mar 1838 | Huron, Sandusky |
| Fairfield | 9 Dec 1800 | Ross, Washington |
| Fayette | 19 Feb 1810 | Ross, Highland |
| Franklin | 30 Mar 1803 | Ross |
| Fulton | 28 Feb 1850 | Lucas, Henry, Williams |
| Gallia | 25 Mar 1803 | Washington, Adams |
| Geauga | 31 Dec 1805 | Trumball |
| Greene | 24 Mar 1803 | Hamilton, Ross |
| Guernsey | 31 Jan 1810 | Belmont, Muskingum |
| Hamilton | 2 Jan 1790 | Original County |
| Hancock | 12 Feb 1820 | Logan |
| Hardin | 12 Feb 1820 | Logan |
| Harrison | 2 Jan 1813 | Jefferson, Tuscarawas |
| Henry | 12 Feb 1820 | Shelby |
| Highland | 18 Feb 1805 | Ross, Adams, Clermont |
| Hocking | 3 Jan 1818 | Athens, Ross, Fairfield |
| Holmes | 20 Jan 1824 | Coshocton, Wayne, Tuscarawas |
| Huron | 7 Feb 1809 | Portage, Cuyahoga |
| Jackson | 12 Jan 1816 | Scioto, Gallia, Athens, Ross |
| Jefferson | 27 Jul 1797 | Washington |
| Knox | 30 Jan 1808 | Fairfield |
| Lake | 6 Mar 1840 | Geauga, Cuyahoga |
| Lawrence | 21 Dec 1815 | Gallia, Scioto |
| Licking | 30 Jan 1808 | Fairfield |
| Logan | 30 Dec 1817 | Champaign |
| Lorain | 26 Dec 1822 | Huron, Cuyahoga, Medina |
| Lucas | 20 Jun 1835 | Wood, Sandusky, Henry |
| Madison | 16 Feb 1810 | Franklin |
| Mahoning | 16 Feb 1846 | Columbiana, Trumball |
| Marion | 12 Feb 1820 | Delaware |
| Medina | 18 Feb 1812 | Portage |
| Meigs | 21 Jan 1819 | Gallia, Athens |
| Mercer | 12 Feb 1820 | Darke |
| Miami | 16 Jan 1807 | Montgomery |
| Monroe | 29 Jan 1813 | Belmont, Washington, Guernsey |
| Montgomery | 24 Mar 1803 | Hamilton, Wayne (old) |
| Morgan | 29 Dec 1817 | Washington, Guernsey, Muskingum |
| Morrow | 24 Feb 1848 | Knox, Marion, Delaware, Richland |
| Muskingum | 7 Jan 1804 | Washington, Fairfield |
| Noble< | 11 Mar 1851 | Monroe, Washington, Morgan, Guernsey |
| Ottawa | 6 Mar 1840 | Erie, Sandusky, Lucas |
| Paulding | 12 Feb 1820 | Darke |
| Perry | 26 Dec 1817 | Washington, Fairfield, Muskingum |
| Pickaway | 12 Jan 1810 | Ross, Fairfield, Franklin |
| Pike | 4 Jan 1815 | Ross, Scioto, Adams |
| Portage | 10 Feb 1807 | Trumball |
| Preble | 15 Feb 1808 | Montgomery, Butler |
| Putnam | 12 Feb 1820 | Shelby |
| Richland | 30 Jan 1808 | Fairfield |
| Ross | 20 Aug 1798 | Adams, Washington |
| Sandusky | 12 Feb 1820 | Huron |
| Scioto | 24 mar 1803 | Adams |
| Seneca | 12 Feb 1820 | Huron |
| Shelby | 7 Jan 1819 | Miami |
| Stark | 13 Feb 1808 | Columbiana |
| Summit | 3 Mar 1840 | Portage, Medina, Stark |
| Trumball | 10 Jul 1800 | Jeferson, Wayne (old) |
| Tuscarawas | 13 feb 1808 | Muskingum |
| Union | 10 Jan 1820 | Franklin, Madison, Logan, Delaware |
| Van Wert | 12 Feb 1820 | Darke |
| Vinton | 23 Mar 1850 | Gallia, Athens, Ross, Jackson, Hocking |
| Warren | 24 Mar 1803 | Hamilton |
| Washington | 27 Jul 1788 | Original County |
| Wayne | 13 Feb 1808 | Columbinana |
| Wayne (old) | 15 Aug 1786 | Original County (became part of Michigan in 1803) |
| Williams | 12 Feb 1820 | Darke |
| Wood | 12 Feb 1820 | Logan |
| Wyandot | 3 Feb 1845 | Marion, Crawford, Hardin, Hancock |
The counties shown above in red were included in the Historical Records Survey conducted by the WPA between the years of 1936 to 1943.
The Historical records Survey compiled indexes of cemetery internments, military records, maps, newspapers, school records, vital statics, etc.
The Genealogical Publishing Company, Baltimore, MD, published a book entitled the Check List of Historical Records Survey Publications, Bibliography of Research Projects Reports, by Sargent B. Child and Dorothy B. Holmes.