1850 Counties of Ohio
| County | Description | Area in sq miles | Courts held at | Pop in 1850 |
| Adams | southern part, on Ohio river | 550 | Adamsvile & West Union | 18,853 |
| Allen | northwest part, water by Auglaize, St Mary's & Miami rivers | 554 | Lima | 12,109 |
| Ashland | northern part | blank | Ashland | 23,811 |
| Ashtabula | northeast part on Lake Erie, water by Grand & Ashtabula river | 700 | Jefferson | 28,766 |
| Athens | southeast part, next to Ohio river & crossed by Hockkocking river | 900 | Athens | 18,215 |
| Auglaize | western part | blank | Wapaukonetta | 11,344 |
| Belmont | in east part, on west died of Ohio river | 500 | St Clairsville | 34,600 |
| Brown | south boundary, on north side of Ohio river | 470 | Georgetown | 27,332 |
| Butler | southwest part, crossed by Miami river & the Miami canal | 480 | Hamilton | 30,789 |
| Carroll | eastern part | 400 | Carrollton | 17,685 |
| Champaign | western part, crossed by Mud river | 450 | Urbana | 19,762 |
| Clermont | southern boundary, on north side of Ohio river | 450 | Batavia | 30,455 |
| Clinton | southwest corner, drained by tributaries of Little Miami river | 400 | Wilmington | 18,838 |
| Columbiana | east boundary, Ohio river on southeast | 750 | New Lisbon | 33,621 |
| Coshocton | near central part | 562 | Coshocton | 25,674 |
| Crawford | north part, drained by Sandusky river | 590 | Bueyrus | 18,177 |
| Cuyahoga | northern boundary on Lake Erie, crossed by Cuyahoga river | 475 | Cleveland | 48,099 |
| Darke | western boundary | 714 | Greenville | 20,274 |
| Defiance | west boundary, crossed by Maumee river | blank | Defiance | 6,966 |
| Delaware | central part, water by Scioto & Whetstone rivers | 610 | Delaware | 21,817 |
| Erie | northern boundary, south of Lake Erie | 150 | Sandusky | 18,568 |
| Fairfield | southeast part | 54 | Lancaster | 30,264 |
| Fayette | southern part | 415 | Washington | 12,726 |
| Franklin | central part, crossed by Scioto river | 529 | Columbus | 42,910 |
| Fulton | northern boundary | blank | Gorham | 7,781 |
| Gallia | south eastern boundary, Ohio river on east | 500 | Gallipolis | 17,063 |
| Geauga | north eastern part | 576 | Chardon | 17,827 |
| Greene | southwest part, crossed by Little Miami & Mad rivers | 400 | Xenia | 22,946 |
| Guernsey | eastern part, valley of Wells creek | 676 | Cambridge | 30,438 |
| Hamilton | southwest corner, Ohio river on south, crossed by Miami & Little Miami rivers & Miami canal | 400 | Cincinnati | 156,843 |
| Hancock | northwest part | 576 | Finley | 11,751 |
| Hardin | northwestern part | 480 | Kenton | 8,265 |
| Harrison | eastern part | 486 | Cadiz | 20,158 |
| Henry | north western part, crossed by Maumee river | 576 | Napoleon | 3,435 |
| Highland | southern part | 555 | Hillsborough | 25,781 |
| Hocking | southern part, crossed by Hocking river | 432 | Logan | 14,119 |
| Holmes | north eastern part | 422 | Millersburgh | 20,452 |
| Huron | northern part | 800 | Norwalk | 26,203 |
| Jackson | southern part | 400 | Jackson | 12,621 |
| Jefferson | east boundary on Ohio river | 396 | Steubenville | 29,132 |
| Knox | central part | 618 | Mount Vernon | 28,773 |
| Lake | north boundary on Lake Erie | 820 | Painesville | 14,650 |
| Lawrence | southern boundary, Ohio river on south | 430 | Burlington | 15,726 |
| Licking | central part | 666 | Newark | 38,852 |
| Logan | toward west part | 425 | Bellefontaine | 19,162 |
| Lorain | northern boundary, on Lake Erie | 540 | Elyria | 26,086 |
| Lucas | northern boundary, Maumee river on southeast | 600 | Maumee City | 12,263 |
| Madison | central part | 400 | London | 10,046 |
| Mohoning | eastern boundary | blank | Canfield | 23,735 |
| Marion | toward north part | 460 | Marion | 12,618 |
| Medina | north part | 450 | Medina | 24,441 |
| Meigs | southeastern boundary on Ohio river | 425 | Pomeroy | 17,969 |
| Mercer | western boundary | 576 | Celina | 7,712 |
| Miami | western part, crossed by Miami river | 410 | Troy | 24,996 |
| Monroe | southeastern boundary, Ohio river on southeast | 520 | Woodsfield | 28,151 |
| Montgomery | southwest part, crossed by Miami river | 480 | Dayton | 38,219 |
| Morgan | southeastern part, crossed by Muskingum river | 500 | M'Connelsville | 28,585 |
| Morrow | central part | blank | Mount Gilead | 20,280 |
| Muskingum | southeast part, crossed by Muskingum river | 665 | Zanesville | 45,037 |
| Noble | southeast part, water by branches of Will's creek; Muskingum & Ohio rivers | 450 | Sarahsville | organized since 1850 |
| Ottawa | northern boundary, Lake Erie on north, Sandusky bay on southeast | 350 | Port Clinton | 3,308 |
| Perry | central part | 400 | Somerset | 20,775 |
| Pickaway | central part, crossed by Scioto river | 470 | Circleville | 21,008 |
| Pike | south part, crossed by Scioto river | 421 | Piketon | 10,953 |
| Portage | in northeastern part, crossed by Cuyahoga & Tuscarawas rivers, which are separated by a portage of one mile | 500 | Ravenna | 24,419 |
| Preble | on west boundary | 432 | Eaton | 21,736 |
| Putnam | northwest part, crossed by Auglaize river | 376 | Kalida | 7,221 |
| Richland | toward northern part | 900 | Mansfield | 30,879 |
| Ross | toward southern part, crossed by Scioto river | 650 | Chillicothe | 32,071 |
| Sandusky | north part, Sandusky bay on northeast, crossed by Sanducky river | 320 | Fremont | 14,305 |
| Scioto | on southern boundary, Ohio river on south, crossed by Scioto river | 600 | Portsmouth | 18,438 |
| Seneca | north part, crossed by Sandusky river | 540 | Tiffin | 37,105 |
| Shelby | western part, crossed by Miami river | 418 | Sidney | 13,958 |
| Stark | in east part, crossed by Tuscarawas river | 650 | Canton | 39,878 |
| Summit | in northeast part, crossed by Cuyahoga river | 422 | Akron | 27,485 |
| Trumbull | east boundary, crossed by Mahoning river | 875 | Warren | 30,491 |
| Tuscarawas | eastern part, crossed by Tuscarawas river | 655 | New Philadelphia | 31,161 |
| Union | toward western part | 450 | Marysville | 12,204 |
| Van Wert | on west boundary | 432 | Van Wert | 4,816 |
| Vinton | in southern part | blank | McArthur | 9,353 |
| Warren | in southwest part, crossed by Little Miami river | 400 | not given | 25,571 |
| Washington | on southeast boundary, Ohio river on southeast, crossed by Muskingum river | 713 | Marietta | 29,540 |
| Wayne | toward northeast part | 660 | Wooster | 32,981 |
| Williams | at northwest corner | 600 | Bryan | 8,018 |
| Wood | in north part, Maumee river on northwest | 590 | Perrysburgh | 9,257 |
| Wyandott | toward north part | blank | Upper Sandusky | 11,292 |