Feature Name | Class | Elev. meters | County | Latitude DMS | Longitude DMS |
| Orville Wright Elementary School for Integrated Leaning | School | 257 | Montgomery | 39 45 44 N | 084 08 32 W |
| Orville Wright Park | Park | 274 | Montgomery | 39 45 41 N | 084 08 24 W |
| Orwell | Populated Place | 273 | Ashtabula | 41 32 06 N | 080 52 05 W |
| Orwell Post Office | Post Office | 273 | Ashtabula | 41 32 05 N | 080 52 04 W |
| Orwell State Wildlife Area | Park | 284 | Ashtabula | 41 33 45 N | 080 50 39 W |
| Orwell Station (historical) | Locale | 285 | Ashtabula | 41 32 06 N | 080 50 54 W |
| Osage | Populated Place | 358 | Jefferson | 40 28 28 N | 080 43 19 W |
| Osage Cemetery | Cemetery | 356 | Jefferson | 40 28 26 N | 080 43 24 W |
| Osage Church | Church | 355 | Jefferson | 40 28 26 N | 080 43 23 W |
| Osage Lake | Reservoir | 348 | Medina | 41 03 48 N | 081 46 29 W |
| Osage Lake Dam | Dam | 348 | Medina | 41 03 48 N | 081 46 29 W |
| Osage Post Office (historical) | Post Office | 365 | Jefferson | 40 28 30 N | 080 43 19 W |
| Osage School | School | 268 | Hamilton | 39 06 32 N | 084 34 02 W |
| Osborn Corners | Populated Place | 320 | Summit | 41 12 06 N | 081 40 43 W |
| Osborn Corners Cemetery | Cemetery | 322 | Summit | 41 12 08 N | 081 40 45 W |
| Osborn Elementary School | School | 315 | Ashland | 40 52 04 N | 082 18 18 W |
| Osborn Park | Park | 256 | Greene | 39 49 00 N | 084 00 58 W |
| Osborn Recreation Area | Park | 178 | Erie | 41 24 55 N | 082 37 60 W |
| Osborn State Farm | Locale | 183 | Erie | 41 24 54 N | 082 38 11 W |
| Osborne Cemetery | Cemetery | 284 | Warren | 39 19 21 N | 084 00 14 W |
| Osborne Hall | Building | 358 | Stark | 40 49 31 N | 081 22 40 W |
| Osborne Park | Park | 181 | Erie | 41 25 03 N | 082 38 23 W |
| Osborne Run | Stream | | Lawrence | 38 33 31 N | 082 43 35 W |
| Osborne School (historical) | School | 278 | Clermont | 39 09 32 N | 084 03 50 W |
| Oscar T Hawke School | School | 273 | Clark | 39 54 47 N | 083 59 55 W |
| Osceola | Populated Place | 238 | Warren | 39 20 30 N | 084 03 19 W |
| Oscola Post Office | Post Office | 283 | Crawford | 40 50 40 N | 083 05 40 W |
| Osgood | Populated Place | 293 | Darke | 40 20 23 N | 084 29 43 W |
| Osgood Post Office | Post Office | 292 | Darke | 40 20 25 N | 084 29 45 W |
| Osman School (historical) | School | 269 | Adams | 38 42 50 N | 083 33 37 W |
| Osman School (historical) | School | 171 | Adams | 38 46 54 N | 083 27 24 W |
| Ostendorf School (historical) | School | 227 | Putnam | 40 55 04 N | 084 16 50 W |
| Osteopathic Hospital | Hospital | 306 | Mahoning | 41 07 00 N | 080 38 39 W |
| Ostrander | Populated Place | 284 | Delaware | 40 15 58 N | 083 12 46 W |
| Ostrander Post Office | Post Office | 282 | Delaware | 40 16 00 N | 083 12 45 W |
| Oswalt Aerodrome Airport | Airport | 364 | Richland | 40 55 12 N | 082 28 45 W |
| Oswalt Ditch | Canal | 222 | Paulding | 41 13 55 N | 084 44 60 W |
| Oswego Cemetery | Cemetery | 319 | Scioto | 38 49 03 N | 083 12 38 W |
| Oswego Church | Church | 317 | Scioto | 38 49 02 N | 083 12 37 W |
| Oswego Ridge | Ridge | 302 | Scioto | 38 50 10 N | 083 11 57 W |
| Oswego School (historical) | School | 322 | Scioto | 38 49 12 N | 083 12 30 W |
| Othneil Looker Park | Park | 161 | Hamilton | 39 15 22 N | 084 48 34 W |
| Otho (historical) | Populated Place | 217 | Morgan | 39 40 52 N | 081 41 51 W |
| Otho Post Office (historical) | Post Office | 223 | Morgan | 39 40 50 N | 081 41 49 W |
| Otis Elementary School | School | 192 | Sandusky | 41 21 16 N | 083 08 53 W |
| Otis Hospital | Hospital | 267 | Mercer | 40 32 57 N | 084 33 54 W |
| Otis Terminal | Building | 196 | Cuyahoga | 41 29 56 N | 081 42 02 W |
| Otsego | Populated Place | 240 | Muskingum | 40 07 17 N | 081 45 53 W |
| Otsego | Populated Place | 191 | Wood | 41 26 51 N | 083 46 45 W |
| Otsego Baptist Church | Church | 243 | Muskingum | 40 07 24 N | 081 45 40 W |
| Otsego Cemetery | Cemetery | 191 | Wood | 41 26 40 N | 083 46 58 W |
| Otsego High School | School | 201 | Wood | 41 25 19 N | 083 44 37 W |
| Otsego Methodist Cemetery | Cemetery | 240 | Muskingum | 40 07 27 N | 081 45 48 W |
| Otsego Methodist Church | Church | 241 | Muskingum | 40 07 27 N | 081 45 47 W |
| Otsego Post Office (historical) | Post Office | 245 | Muskingum | 40 07 20 N | 081 45 54 W |
| Ottawa | Populated Place | 222 | Putnam | 41 01 09 N | 084 02 50 W |
| Ottawa City Hall | Building | 222 | Putnam | 41 01 12 N | 084 02 49 W |
| Ottawa County | Civil | 177 | Ottawa | 41 32 00 N | 083 06 00 W |
| Ottawa County Courthouse | Building | 178 | Ottawa | 41 30 35 N | 082 56 26 W |
| Ottawa County Fairgrounds | Locale | 175 | Ottawa | 41 30 25 N | 083 05 07 W |
| Ottawa County Home | Locale | 175 | Ottawa | 41 30 23 N | 083 05 31 W |
| Ottawa County Law Library | Building | 178 | Ottawa | 41 30 35 N | 082 56 26 W |
| Ottawa County Nursing Home | Building | 175 | Ottawa | 41 30 23 N | 083 05 27 W |
| Ottawa Creek | Stream | | Delaware | 40 23 55 N | 083 11 44 W |
| Ottawa Creek | Stream | | Hancock | 41 02 17 N | 083 48 05 W |
| Ottawa Elementary School | School | 223 | Putnam | 41 01 20 N | 084 02 23 W |
| Ottawa Hills | Populated Place | 184 | Lucas | 41 39 51 N | 083 38 36 W |
| Ottawa Hills Elementary School | School | 190 | Lucas | 41 40 02 N | 083 37 45 W |
| Ottawa Hills High School | School | 190 | Lucas | 41 40 12 N | 083 37 54 W |
| Ottawa National Wildlife Refuge | Park | 175 | Ottawa | 41 36 56 N | 083 12 58 W |
| Ottawa Park | Park | 185 | Lucas | 41 40 03 N | 083 35 58 W |
| Ottawa Point Reserved Picnic Area | Locale | 248 | Cuyahoga | 41 18 05 N | 081 35 59 W |
| Ottawa Post Office | Post Office | 222 | Putnam | 41 01 08 N | 084 02 38 W |
| Ottawa Prairie | Area | 216 | Sandusky | 41 16 00 N | 083 20 60 W |
| Ottawa River | Stream | | Lucas | 41 44 30 N | 083 27 40 W |
| Ottawa River | Stream | | Putnam | 40 59 42 N | 084 14 29 W |
| Ottawa River Cemetery | Cemetery | 228 | Putnam | 40 54 22 N | 084 12 29 W |
| Ottawa River Church | Church | 227 | Putnam | 40 54 21 N | 084 12 29 W |
| Ottawa River Elementary School | School | | Lucas | 41 42 34 N | 083 29 11 W |
| Ottawa River High School | School | 177 | Lucas | 41 42 34 N | 083 29 14 W |
| Ottawa River United Methodist Church | Church | 176 | Lucas | 41 43 15 N | 083 29 53 W |
| Ottawa River Yacht Club | Locale | 175 | Lucas | 41 43 34 N | 083 28 05 W |
| Ottawa School (historical) | School | 279 | Delaware | 40 24 14 N | 083 13 22 W |
| Ottawa Shooting Club | Locale | 175 | Sandusky | 41 26 18 N | 083 02 16 W |
| Ottawa Upground Reservoir | Reservoir | 221 | Putnam | 41 00 48 N | 084 01 12 W |
| Ottawa Upground Reservoir Dam | Dam | 221 | Putnam | 41 00 48 N | 084 01 12 W |
| Ottawa Valley Hospital | Hospital | 267 | Allen | 40 43 20 N | 084 08 33 W |
| Ottawa Water Works | Building | 224 | Putnam | 41 01 17 N | 084 02 12 W |
| Ottawa-Glandorf High School | School | 223 | Putnam | 41 01 44 N | 084 02 45 W |
| Otter | Populated Place | 310 | Union | 40 16 33 N | 083 25 09 W |
| Otter Creek | Stream | | Logan | 40 21 35 N | 083 32 40 W |
| Otter Creek | Stream | | Lucas | 41 41 50 N | 083 27 13 W |
| Otter Creek | Stream | | Marion | 40 35 29 N | 082 59 03 W |
| Otter Fork Licking River | Stream | | Licking | 40 15 12 N | 082 32 04 W |
| Otter Island | Island | 190 | Wood | 41 26 55 N | 083 46 51 W |
| Otter Run | Stream | | Noble | 39 45 19 N | 081 31 17 W |
| Otter Run | Stream | | Union | 40 16 54 N | 083 23 20 W |
| Otter School (historical) | School | 264 | Wyandot | 40 55 09 N | 083 27 44 W |
| Otterbein | Populated Place | 338 | Darke | 39 56 45 N | 084 40 18 W |
| Otterbein | Populated Place | 296 | Hardin | 40 35 03 N | 083 30 20 W |
| Otterbein | Populated Place | 270 | Warren | 39 26 46 N | 084 16 41 W |
| Otterbein Cemetery | Cemetery | 337 | Darke | 39 56 43 N | 084 40 14 W |
| Otterbein Cemetery | Cemetery | 257 | Franklin | 40 07 18 N | 082 56 07 W |
| Otterbein Cemetery | Cemetery | 297 | Hardin | 40 35 02 N | 083 30 16 W |
| Otterbein Cemetery | Cemetery | 281 | Marion | 40 29 31 N | 083 11 41 W |
| Otterbein Cemetery | Cemetery | 252 | Mercer | 40 39 20 N | 084 38 17 W |
| Otterbein Cemetery | Cemetery | 312 | Perry | 39 46 19 N | 082 21 48 W |
| Otterbein Cemetery | Cemetery | 329 | Vinton | 39 21 31 N | 082 34 50 W |
| Otterbein Chapel | Church | 325 | Vinton | 39 21 30 N | 082 34 58 W |
| Otterbein Chapel Cemetery | Cemetery | 239 | Hocking | 39 34 47 N | 082 17 59 W |