Creator
- Northwestern Terra Cotta Company1
- O.W. Ketcham Terra Cotta Works1
- Office of Sylvan Bien1
- Olmsted Brothers1
- Ording, C1
- Pelham, George F (George Frederick), 1866-19371
- Pelham, George Fred, -19671
- Pilcher, Lewis F1
- Platt, Charles A (Charles Adams), 1861-19331
- Post, George Browne, 1837-19131
- Potter, Wilson1
- Prince, Harry M1
- Proudfoot, Bird and Rawson1
- R. E. Dowling Realty Corp1
- Raritan Clay Co1
- Reed & Stem1
- Renwick, Aspinwall & Tucker1
- Richard Gluckman Architects1
- Richards, McCarty & Bulford (Columbus, Ohio)1
- Ritz-Carlton Hotels (Firm)1