Massachusetts - Area of significance: Architecture
| Old Medford High School |
| Old Mill |
| Old North Cemetery |
| Old North Church |
| Old Post Office Building |
| Old Post Office Building |
| Old Public Library |
| Old Shephard Farm |
| Old Shipbuilder's Historic District |
| Old Ship Meetinghouse |
| Old Ship Street Historic District |
| Old South Church in Boston |
| Old South Meeting House |
| Old South Union Church |
| Old State House |
| Old State Mutual Building |
| Old Third District Courthouse |
| Old Town Center Historic District |
| Old Town Farm |
| Old Town Hall |
| Old Town Hall |
| Old Town Hall Historic District |
| Old Town Hall Historic District |
| Old Town Historic District |
| Old Village Historic District |
| Old Weir Stove Company |
| Old West Church |
| Oliver House |
| Olmsted-Hixon-Albion Block |
| Olmsted Subdivision Historic District |
| Olney Cook Artisan Shop |
| Opposition House |
| Orange Armory |
| Orange Center Historic District |
| Original Congregational Church of Wrentham |
| Orlando |
| Orne, Sarah, House |
| Orrock, Rev. John, House |
| Orvis Road Historic District |
| Osborn, Benjamin, House |
| Osborne, Prince, House |
| Osborn House |
| Osborn Street School |
| Osgood Bradley Building |
| Osgood, Col. John, House |
| Osgood Farm |
| Osgood Hill |
| Osgood, Samuel, House |
| O'Shea Building |
| Osterville Baptist Church |
| Otis Center Historic District |
| Otis Company Mill No. 1 |
| Otis, (First) Harrison Gray, House |
| Otis, (Second) Harrison Gray, House |
| Otis-Wyman House |
| Our Lady Help of Christians Historic District |
| Our Lady of Good Voyage Church |
| Our Mother of Sorrows Monastery and Retreat Center |
| Outing Park Historic District |
| Oxford-Crown Extension District |
| Oxford-Crown Historic District |
| Oxford Main Street Historic District |
| Oxford School |
| Oxford, The |
| Packard, Moses, House |
| Padanaram Village Historic District |
| Paddock Farm |
| Page, Christopher, House |
| Page, H. P., House |
| Page, Nathaniel, House |
| Page, Thomas D., House |
| Paine-Dodge House |
| Paine Estate |
| Paine Furniture Building |
| Paine Hollow Road South Historic District |
| Paine, Robert Treat, Jr., House |
| Paine, Timothy, House |
| Palmer Island Light Station |
| Palmer Memorial Hall |
| Palmer School |
| Pan Historic District |
| Park Building |
| Parker-Burnett House |
| Parker, Capt. Nathaniel, Red House |
| Parker, Edmund, Jr., House |
| Parker, Harrison, Sr., House |
| Parker House |
| Parker House |
| Parker House |
| Parker, James, House |
| Parker, Joseph, House |
| Parker, Samuel, House |
| Parker, Stillman, House |
| Parker Tavern |
| Parker Village Historic District |
| Parker, William, House |
| Parkhill Mill |
| Park Lodge |
| Parkman Tavern |
| Park Square Historic District |
Data from United States Park Service and Wikidata
