Ohio - Criteria: A (event)
| Ohio Institution for the Education of the Deaf and Dumb |
| Ohio Lantern Company |
| Ohio Moline Plow Company Building |
| Ohio One-Ohio Edison |
| Ohio Soldiers' And Sailors' Home |
| Ohio Stadium |
| Ohio Statehouse |
| Ohio State Normal College At Kent |
| Ohio State Reformatory |
| Ohio Theatre |
| Ohio Theatre |
| Ohio Wesleyan University Student Observatory |
| Old Beechwold Historic District |
| Old City Hall |
| Old District 10 Schoolhouse |
| Old Elyria Water Tower |
| Old Euclid District 4 Schoolhouse |
| Old Governor's Mansion |
| Old Harbour Store |
| Old Hotel, The |
| Old Lawrence County Jail |
| Old McKinley High School |
| Old Meigs County Courthouse And Chester Academy |
| Old Ohio Union |
| Old Port Columbus Airport Control Tower |
| Old Post Office And Federal Building |
| Old School Privy |
| Old St. Mary's Church, School and Rectory |
| Old Union School |
| Old US Post Office |
| Old Wayne County Jail |
| Old Wood County Jail |
| Olive Branch High School |
| Olive Furnace |
| Olney, Charles, House and Gallery |
| Omar Chapel |
| O'Neil's Department Store |
| Onesto Hotel |
| Oppmann Terrace |
| O'Shaughnessy Dam and Bridge |
| Otis Hospital |
| Ottawa Waterworks Building |
| Ourant's School |
| Our House |
| Our Lady of Mount Carmel Church |
| Outville Depot |
| Outville Hay and Grain Company Building |
| Overfield Tavern |
| Overmyer-Waggoner-Roush Farm |
| Over-the-Rhine Historic District |
| Oxford Female Institute |
| Oxford Railroad Depot and Junction House |
| Ozmun, Isaac and Maria, Farmstead |
| Packard-Doubler House |
| Painesville City Hall |
| Palace Theater |
| Palace Theater |
| Palace Theatre |
| Palmyra Center Hotel |
| Palos Covered Bridge |
| Parks Covered Bridge |
| Parkside Apartments |
| Patterson, Mary A., Memorial |
| Paulding County Carnegie Library |
| Paul Hall, Muskingum College |
| Peairs Homestead |
| Peeble's Corner Historic District |
| Peggy Ann Building |
| Peninsula Village Historic District |
| Pennsylvania Depot |
| Pennsylvania House |
| Pennsylvania Railroad Depot And Baggage Room |
| Pennsylvania Railway Station |
| Perry County Courthouse and Jail |
| Petersburg Mill |
| Peters Cartridge Company |
| Phoenix Building/Cincinnati Club |
| Pickerington Carnegie Library |
| Pickerington Depot |
| Picking, D., And Company |
| Pilgrim Congregational Church |
| Pilgrim Presbyterian Church |
| Piqua-Caldwell Historic District |
| Piqua High School |
| Pittsburg, Cincinnati, and St. Louis Depot |
| Playhouse Square Group |
| Plum Street Temple |
| Point, Nathaniel, Farm |
| Poland Center School |
| Police Station No. 2 |
| Police Station No. 3 |
| Police Station No. 5 |
| Police Station No. 6 |
| Police Station No. 7 |
| Port Clinton City Hall |
| Port Jefferson School |
| Port Washington Town Hall |
| Potters National Bank |
| Potters Savings and Loan |
| Powell, Andrew, Homestead |
Data from United States Park Service and Wikidata
