Pennsylvania - Area of significance: Industry
| Mecky, A., Company Building |
| Meinig Glove Factory-Meinig, E. Richard, Co. |
| Merchants Cigar Box Company |
| Merkel Mill |
| Merkel Mill Complex |
| Metz Ice Plant |
| Meyerhoff, Son and Company Building |
| Middishade Clothing Factory |
| Mifflinburg Historic District |
| Milanville Historic District |
| Mill at Lobachsville |
| Mill Creek Historic District |
| Miller, David H., Tobacco Warehouse |
| Milleysack, J. B. Cigar Factory |
| Millheim Historic District |
| Millionaire's Row Historic District |
| Milton Historic District |
| Mine Roof Simulator |
| Minersville Historic District |
| Modern Tool Company |
| Monroe Furnace |
| Moselem Farms Mill |
| Mount Airy Historic District |
| Mount Hope Estate |
| Mount Joy |
| Mount Pleasant Historic District |
| Mount St. Peter Roman Catholic Church |
| Mount Union Historic District |
| Mount Vernon Furnace |
| Moxham Historic District |
| Mt. Pleasant Iron Works House |
| Muddy Creek Forks Historic District |
| Muhlenberg, Henry Melchoir, House |
| Mumma, Samuel N., Tobacco Warehouse |
| Neuweiler Brewery |
| New Geneva Historic District |
| New Hamburg Historical Area |
| New Holland Machine Company |
| New Hope Village District |
| New Kensington Downtown Historic District |
| New Kensington Production Works Historic District |
| Newlin Miller's House |
| Newport Historic District |
| Nissly-Stauffer Tobacco Warehouses |
| Nissly Swiss Chocolate Company |
| Nitre Hall |
| Northern Liberties Historic District |
| North Hill Historic District |
| North Prince Street Historic District |
| North Warwick Historic and Archeological District |
| N. Shippen-Tobacco Avenue Historic District |
| Oak Hill Estate |
| O'Connor, J.S., American Rich Cut Glassware Factory |
| Oil City Downtown Commercial Historic District |
| Oil City North Side Historic District |
| Oil City South Side Historic District |
| Old Conemaugh Borough Historic District |
| Old Mauch Chunk Historic District |
| Old Pottstown Historic District |
| Old Waterworks |
| Old White Mill |
| Oley Township Historic District |
| Oregon Mill Complex |
| Orris, Adam, House |
| Orthodox Meetinghouse |
| Otto Eisenlohr and Bros Cigar Factory |
| Packer, Asa, Mansion |
| Paradise Furnace |
| Patterson, Burd, House |
| Patton Historic District |
| Peerless Furniture Company |
| Pennsalt Historic District |
| Pennsylvania Furnace Mansion |
| Pennsylvania Match Company |
| Peters-Graham House |
| Peter Woll and Sons Factory |
| Philips, Hardman, House |
| Phillips Mill Historic District |
| Phoenixville Historic District |
| Pine Forge Mansion and Industrial Site |
| Pine Grove Furnace |
| Pitcairn Building |
| Pithole City, Site of |
| Pittsburgh Brass Manufacturing Company Building |
| Poole Forge |
| Potter-Allison Farm |
| Pottstown Roller Mill |
| Pottsville Downtown Historic District |
| Powelton Historic District |
| Pringle Electrical Manufacturing Company Building |
| Prizer's Mill Complex |
| Progress Lighting Manufacturing Company |
| Pusey-Crozier Mill Historic District |
| Quaker City Dye Works |
| Quarries of the Hummelstown Brownstone Company |
| Railroad Borough Historic District |
| Ramcat Historic District |
| Reading Hardware Company |
| Reading Hardware Company Butt Works |
| Reading Knitting Mills |
Data from United States Park Service and Wikidata
