Maryland - Role: Building
| Old Town Friends' Meetinghouse |
| Old Town Savings Bank |
| Old Washington County Library |
| Old Wye Church |
| Olney |
| One Charles Center |
| Orchard Street United Methodist Church |
| Orem's Delight |
| Orendorff, John, Farm |
| Otterbein Church |
| Otwell |
| Owens, James, Farm |
| Owings Upper Mill |
| Oxon Hill Manor |
| Ozmon, Capt. John H., Store |
| Paca House and Garden |
| Paca Street Firehouse |
| Panther's Den |
| Paradise Manor |
| Parker Metal Decoration Company Plant |
| Parkhurst |
| Parkton Hotel |
| Paul Laurence Dunbar School Complex |
| Paw Paw Building |
| Peale's Baltimore Museum |
| Pearre-Metcalfe House |
| Peggy Stewart House |
| Pemberton Hall |
| Pennington Cottage |
| Pennsylvania Station |
| Pennterra |
| Perry-Cooper House |
| Perry Hall |
| Phillips Packing Company Plant F |
| Phoenix Mill Farm |
| Pikesville Armory |
| Piney Grove |
| Pinkney-Callahan House |
| Pipe Creek Friends Meetinghouse |
| Piper House |
| Pleasant Hill |
| Pleasant Hills |
| Pleasant Prospect |
| Plinlimmon Farm |
| Plumb Grove |
| Poe, Edgar Allan, House |
| Point of Rocks Railroad Station |
| Polish Home Hall |
| Polychrome Historic District |
| Pomfret Plantation |
| Poole, Nathan Dickerson, House |
| Poplar Hill |
| Poplar Hill Mansion |
| Poppleton Fire Station |
| Portland Manor |
| Porto Bello |
| Potter Hall |
| Pratt Street Power Plant |
| Presbury Meetinghouse |
| President Street Station |
| Preston-on-the-Patuxent |
| Price-Miller House |
| Priest Neal's Mass House and Mill Site |
| Primrose Hill |
| Pritchard, Dr. William B., House |
| Proctor and Gamble Baltimore Plant |
| Proctor House |
| Prospect Hall |
| Prospect Hill |
| Public Safety Building |
| Public School No. 109 |
| Public School No. 111 |
| Public School No. 25 |
| Public School No. 37 |
| Public School No. 99 |
| Puncheon Mill House |
| Purnell, George Washington, House |
| Quarter Place |
| Queenstown Rosenwald School |
| Queponco Railway Station |
| Quindocqua United Methodist Church |
| Radcliffe Mill |
| Ravenshurst |
| Readbourne |
| Reed's Creek Farm |
| Rehobeth Presbyterian Church |
| Rehoboth |
| Remsen, Ira, House |
| Retreat |
| Reward |
| Reward-Tilden's Farm |
| Richards, Thomas, House |
| Rich Hill |
| Rich Hill |
| Richland |
| Richland Farm |
| Rich Mountain |
| Ridgeley School |
| Ridge, The |
| Ridgeton Farm |
Data from United States Park Service and Wikidata
