Ohio - Role: Building
| Odd Fellows Temple |
| Oesterlein Machine Company-Fashion Frocks, Inc. Complex |
| Ohio Asylum for the Blind |
| Ohio Baptist General Association Headquarters |
| Ohio Bell Henderson-Endicott Exchange Building |
| Ohio Bell Southwestern Headquarters |
| Ohio Brass Company Office Building |
| Ohio Company Land Office |
| Ohio Farm Bureau Federation Offices |
| Ohio Finance Building |
| Ohio Hospital For Epileptics Stone Water Towers |
| Ohio Institution for the Education of the Deaf and Dumb |
| Ohio Lantern Company |
| Ohio Moline Plow Company Building |
| Ohio National Bank |
| Ohio National Guard Armory |
| Ohio One-Ohio Edison |
| Ohio Power Company |
| Ohio Soldiers' And Sailors' Home |
| Ohio Stadium |
| Ohio State Arsenal |
| Ohio Statehouse |
| Ohio State Normal College At Kent |
| Ohio State Office Building |
| Ohio State Reformatory |
| Ohio Theatre |
| Ohio Theatre |
| Ohio Theatre |
| Ohio Theatre |
| Ohio Valley Clay Company |
| Ohio Wesleyan University Student Observatory |
| Ohmer, Nicholas, House |
| Old Akron Post Office |
| Old Amherst Freight Depot |
| Old Bartlett and Goble Store |
| Old Carriage Barn |
| Old Center School |
| Old Central Post Office |
| Old City Hall |
| Old College Hill Post Office |
| Old District 10 Schoolhouse |
| Old Euclid District 4 Schoolhouse |
| Old Federal Building and Post Office |
| Old First Church |
| Old Funeral Palor |
| Old Gothic Barns |
| Old Governor's Mansion |
| Old Harbour Store |
| Old Hotel, The |
| Old Interurban Station |
| Old Jib's Corner |
| Old Lawrence County Jail |
| Old Log Post Office |
| Old Mahoning County Courthouse |
| Old McKinley High School |
| Old Meigs County Courthouse And Chester Academy |
| Old Mill |
| Old Ohio Union |
| Old Peace Lutheran Church |
| Old Port Columbus Airport Control Tower |
| Old Post Office And Federal Building |
| Old Railroad Station |
| Old School Privy |
| Old South Church |
| Old St. Mary's Church, School and Rectory |
| Old Stone Church |
| Old St. Patrick's Church |
| Old Union School |
| Old Union School |
| Old US Post Office |
| Old Vermilion Banking Company Building |
| Old Vermilion Mill |
| Old Wayne County Jail |
| Old Wood County Jail |
| Olin, Arvin, House |
| Olive Branch High School |
| Oliver, John G., House |
| Ollie's Tavern |
| Olmsted Falls Depot |
| Olney, Charles, House and Gallery |
| Omar Chapel |
| O'Neil's Department Store |
| Onesto Hotel |
| Ontario Building |
| O. P. Boyer’s and Sons Funeral Home |
| Open Air School |
| Oppmann Terrace |
| Orton Memorial Laboratory |
| Osborn, Charles S., House |
| Osborne School |
| Otis Hospital |
| Ottawa County Courthouse |
| Ottawa Waterworks Building |
| Otterbein Mausoleum |
| Ourant's School |
| Our House |
| Our Lady of Mercy High School |
| Our Lady of Mount Carmel Church |
| Outville Depot |
| Outville Hay and Grain Company Building |
Data from United States Park Service and Wikidata
