Pennsylvania - Criteria: C (architecture/engineering)
| Locust Grove |
| Logan Demonstration School |
| Logan Furnace Mansion |
| Logan Mills Covered Bridge |
| Logans Ferry Powder Works Historic District |
| Logan Square |
| Log House, Hiester House, and Market Annex |
| Longfellow, Henry, School |
| Longfellow School |
| Long-Hawerter Mill |
| Longland |
| Long Meadow Farm |
| Longue Vue Club and Golf Course |
| Longwell, David, House |
| Longwood Gardens District |
| Lorraine Apartments |
| Loux Covered Bridge |
| Lovell Manufacturing Company |
| Lowell, James Russell, School |
| Lower Humbert Bridge |
| Lower Marsh Creek Presbyterian Church |
| Lower Merion Academy-Cynwyd Elementary School-Bala Cynwyd Junior High School Complex |
| Lower North Philadelphia Speculative Housing Historic District |
| Lower Swedish Cabin |
| Lowrie, Sen. Walter, House |
| Ludlow, James R., School |
| Lukens Main Office Building |
| Lunn's Tavern |
| Lutz-Franklin School |
| Lutz, John F., Furniture Co. & Funerary |
| Luzerne County Courthouse |
| Luzerne Presbyterial Institute |
| Lynn Hall |
| Madison Elementary School |
| Madison, James, School |
| Main Building, U.S. Bureau of Mines |
| Main Library |
| Makefield Meeting |
| Malden Inn |
| Malvern Hall |
| Manasses Guth Covered Bridge |
| Manayunk Main Street Historic District |
| Manchester Historic District |
| Manchester, Isaac, House |
| Manheim Borough Historic District |
| Mann, William, School |
| Manor Street Elementary School |
| Mansfield |
| Mansfield Armory |
| Marine Corps Depot of Supplies, Schuykill Warehouse |
| Marion Bridge |
| Market Street Bridge |
| Market Street Bridge |
| Markle Banking & Trust Company Building |
| Marklesburg Historic District |
| Marlborough Village Historic District |
| Marshall, Humphry, House |
| Marshall, John, School |
| Marshall's Bridge |
| Marshall, Thomas, House |
| Marshallton Historic District |
| Marshallton Inn |
| Martin, B. B., Tobacco Warehouse |
| Martin Farmstead |
| Martin, James, School |
| Martin-Little House |
| Martin Orthopedic School |
| Mary Ann Furnace Historic District |
| Mascot Roller Mills |
| Mask and Wig Club of the University of Pennsylvania |
| Masonic Temple |
| Masonic Temple |
| Masonic Temple and Scottish Rite Cathedral |
| Massey, Thomas, House |
| Matlack, Enoch, House |
| Mauch Chunk and Summit Hill Switchback Railroad |
| Mauer, Dr. Joseph House |
| Maxwell, Ebenezer, House |
| Mayfair House |
| McAllister, Archibald, House |
| McAllister-Beaver House |
| McCalls Ferry Farm |
| McCallum Manor |
| McClay's Twin Bridge (East) |
| McClay's Twin Bridge (West) |
| McCleary Elementary School |
| McClelland Homestead |
| McClenathan, J.C., Dr., House and Office |
| McClintock Hall |
| McClure, Alexander K., School |
| McCollum and Post Silk Mill |
| McConnell House |
| McConnellsburg Historic District |
| McConnell's Mill Covered Bridge |
| McCook Family Estate |
| McCormick, John B., House |
| McCoy-Shoemaker Farm |
| McDaniel, Delaplaine, School |
| McDowell Memorial Presbyterian Church |
| McFarlane, Andrew and Jennie, House |
Data from United States Park Service and Wikidata
