All - Architectural style - Federal architecture
| Myers, Moses, House |
| Myrick House |
| Myrtle Hall Farm |
| Myrtle Hill |
| Myrtle Moor |
| Nace (Neas), George, House |
| Napier, Richard C., House |
| National Hotel |
| Neal, James, House |
| Needham |
| Neher-Elseffer House |
| Neibert-Fisk House |
| Neill-Turner-Lester House |
| Nell, William C., House |
| Nelson Homestead |
| Nelson-Reardon-Kennard House |
| Nettleton House |
| Newbill-McElhiney House |
| New Boston Inn |
| New Castle Congregational Church |
| Newcomb, John, House |
| Newcomer Mansion |
| Newell Farm |
| New Ipswich Town Hall |
| Newton, Judge Eben, House |
| Newton, Marvin, House |
| Nicholson House and Inn |
| Nickels-Sortwell House |
| Nicoll, Caroline, House |
| Nightengale, Solomon, House |
| Nitre Hall |
| Noble, John Glover, House |
| Noland, Jesse, House |
| Noon, Philip, House |
| Norman Vale |
| North, Benjamin D., House |
| Northeast School |
| North Wilmot Union Meetinghouse |
| North Yarmouth and Freeport Baptist Meetinghouse |
| Norton, Rev. Asahel, Homestead |
| Norwood |
| Norwood |
| Nutter-Rymes House |
| Nutting Homestead, The |
| Nutwood |
| Oak Crest |
| Oakdale |
| Oakforest |
| Oak Forest |
| Oak Grove |
| Oak Grove |
| Oak Grove |
| Oak Grove |
| Oak Hill |
| Oak Hill |
| Oak Hill |
| Oaklana |
| Oakland |
| Oakland |
| Oakland |
| Oak Lawn |
| Oak Lawn |
| Oakley |
| Oakley |
| Oak Spring Farm |
| Oaks, The |
| Oakwood |
| Oaky Grove |
| Oaterhoudt Stone House |
| Oatlands |
| O'Connor, J.S., American Rich Cut Glassware Factory |
| Octagon, The |
| Oglesby-Conrad |
| O'Hair, James Edington Montgomery, House |
| O'Hara, Mark, House |
| Olcott, John E., House |
| Old Broad Street Presbyterian Church and Cemetery |
| Old Chiswell Place |
| Old City Hall |
| Old Fort House |
| Old Hardy County Courthouse |
| Old Homestead |
| Old Hoosier Theatre |
| Old Indian Agency House |
| Old Kaw Mission |
| Old Meigs County Courthouse And Chester Academy |
| Old Merchant's House |
| Old Queen's |
| Old Richmond County Courthouse |
| Old Riverton Inn |
| Old Rose Tree Tavern |
| Old Seminary Building |
| Old Shephard Farm |
| Old Stone House Library, The |
| Old Town Hall |
| Old Town Hall |
| Old West Church |
| Old West, Dickinson College |
| Oliver House |
| Ollie's Tavern |
Data from United States Park Service and Wikidata
