Maryland - Significance region: Local
| Nanticoke Lodge No. 172, A.F. and A.M. |
| National Brewing Company |
| National Enameling and Stamping Company |
| Neck Meetinghouse and Yard |
| Nelson, Henry, House |
| Nelson Homestead |
| Nelson-Reardon-Kennard House |
| New Mark Commons |
| New Town Center |
| New Windsor Historic District |
| Nicodemus Mill Complex |
| Nolands Ferry I Archeological Site (18FR17) |
| Norman's Retreat |
| Norris-Stirling House |
| North Brentwood Historic District |
| North Central Historic District |
| Northern District Police Station |
| Northwood Historic District |
| Null House |
| Oakdale |
| Oakenshawe Historic District |
| Oak Grove |
| Oak Hill Historic District |
| Oakland |
| Oakland |
| Oakland Historic District |
| Oakland Mills Blacksmith House and Shop |
| Oak Lawn |
| Oaks II |
| Oak Street Garage |
| Oakwood |
| Octorara Farm |
| Odd Fellows Hall |
| O'Dea House |
| Odenton Masonic Lodge No. 209 |
| Old Bloomfield |
| Old Catonsville High School |
| Old Chiswell Place |
| Old Colony Cove Site |
| Old Hamilton Library |
| Old Inn, The |
| Old Pine Street Station |
| Old Town College Park |
| Old Town Savings Bank |
| Old West Baltimore Historic District |
| Old Wye Church |
| Olney |
| One Charles Center |
| Orchard Street United Methodist Church |
| Orendorff, John, Farm |
| Otwell |
| Owens, James, Farm |
| Owensville Historic District |
| Ozmon, Capt. John H., Store |
| Paca Street Firehouse |
| Panther's Den |
| Paradise Manor |
| Park Circle Historic District |
| Parker Metal Decoration Company Plant |
| Park Heights Historic District |
| Parkhurst |
| Parkton Hotel |
| Patterson Park-Highlandtown Historic District |
| Paul Laurence Dunbar School Complex |
| Paw Paw Building |
| Paw Paw Cove Site |
| Peace Cross |
| Pearre-Metcalfe House |
| Pennington Cottage |
| Pennterra |
| Perkins Square Gazebo |
| Perry-Cooper House |
| Perry Hall |
| Phillips Packing Company Plant F |
| Phoenix Mill Farm |
| Pigtown Historic District |
| Pine Street Neighborhood Historic District |
| Piney Grove |
| Piper House |
| Piscataway Park |
| Piscataway Village Historic District |
| Pleasant Hill |
| Pleasant Hills |
| Pleasant Prospect |
| Plinlimmon Farm |
| Plumb Grove |
| Pocomoke City Historic District |
| Point No Point Light Station |
| Polish Home Hall |
| Polychrome Historic District |
| Pomfret Plantation |
| Pomonkey Historic District |
| Poole, Nathan Dickerson, House |
| Poolesville Historic District |
| Poplar Hill |
| Poppleton Fire Station |
| Portland Manor |
| Potomac-Broadway Historic District |
| Potter Hall |
| Pratt Street Power Plant |
Data from United States Park Service and Wikidata
