Pennsylvania - Significance region: Local
| Octagon Stone Schoolhouse |
| O'Donel House and Farm |
| Ogden House |
| Ogontz Hall |
| Ohringer Building |
| Oil City North Side Historic District |
| Oil City South Side Historic District |
| Okehocking Historic District |
| Old Allegheny Rows Historic District |
| Old Conemaugh Borough Historic District |
| Old Downtown Harrisburg Commercial Historic District |
| Old Dry Road |
| Old Heidelberg Apartments |
| Old Homestead |
| Old Hoopes School |
| Old Indiana County Courthouse |
| Old Indiana County Jail and Sheriff's Office |
| Old Lehigh County Courthouse |
| Old Main at the Lutheran Home at Topton |
| Old Main, California State College |
| Old Main, Goethean Hall, and Diagnothian Hall |
| Old Mauch Chunk Historic District |
| Old Norriton Presbyterian Church |
| Old Pottstown Historic District |
| Old Stone Arch Bridge |
| Old Town Historic District |
| Old Uptown Harrisburg Historic District |
| Old White Mill |
| Oliver, David P., High School |
| Oller, Joseph J., House |
| Olney Elementary School |
| Olney High School |
| Oregon Mill Complex |
| Ormrod, George, House |
| Orris, Adam, House |
| Ortlieb, Henry F., Company Bottling House |
| Orton, Almerion C. & Barbara Moseman, Farm |
| Osterburg Covered Bridge |
| Osterling, Frederick J., Office and Studio |
| Otto Eisenlohr and Bros Cigar Factory |
| Overbrook Farms |
| Overbrook Gardens Apartments |
| Overbrook High School |
| Overbrook School |
| Oxford Historic District |
| Oxford Hotel |
| Oyer, Christian, Jr., House |
| Packer, Harry, Mansion |
| Packer, Isaac A., Farm |
| Packer Memorial Chapel |
| Packsaddle Bridge |
| Packwood House-American Hotel |
| Pagoda |
| Painter’s Folly |
| Palmer, Amos, House |
| Palmerton Historic District |
| Paoli Battlefield Site and Parade Grounds |
| Paradise Furnace |
| Paradise Valley Historic District |
| Pardee, Israel Platt, Mansion |
| Park Dinor |
| Parker's Ford |
| Parkersville Friends Meetinghouse |
| Parkesburg National Bank |
| Parkesburg School |
| Parkhurst Memorial Presbyterian Church |
| Parkinson, Robert, Farm |
| Park Place School |
| Parkside Chapel |
| Parkside Historic District |
| Park Site 36La96 |
| Park Towne Place |
| Parreco, James, House |
| Parr's Mill Covered Bridge No. 10 |
| Passavant House |
| Passmore, Mansel, House |
| Passtown Elementary School |
| Paterson, John M., School |
| Patriotic Order Sons of America Washington Camp 422 |
| Patterson Covered Bridge No. 112 |
| Patterson, Samuel, House |
| Patton Historic District |
| Paupack School |
| Pawling, Isaac, House |
| Paxson, Isaiah, Farm |
| Payne's Folly |
| Peerless Furniture Company |
| Peirce, William S., School |
| Penn Alto Hotel |
| Penn Asylum for Indigent Widows and Single Women |
| Pennell, Joseph, School |
| Penn-Liberty Historic District |
| Pennock E. Sharpless House |
| Pennock, Martha, House |
| Pennsalt Historic District |
| Penn's Cave and Hotel |
| Penn's Park General Store Complex |
| Penns Park Historic District |
| Pennsylvania Canal Guard Lock and Feeder Dam, Raystown Branch |
| Pennsylvania Chautauqua Historic District |
Data from United States Park Service and Wikidata
