- 5 Oregon Avenue
- 4 Organ grinders
- 8 Organ pipes
- 1 Organized effort
- 14 Organs
- 1 Orger, Mary Ann, 1788-1849
- 10 Orianna Street
- 3 Oriental Mills (George Brooks & Son) (Upholstery goods)
- 10 Oriental rugs
- 1 Orientalism
- 2 Origami
- 1 Orinoka Mills Corporation
- 2 Orleans Hotel
- 1 Orleans Street
- 54 Ornaments
- 2 Ornate (typeface group)
- 5 Ornithological illustrations
- 2 Ornithologists
- 1 Ornithology
- 11 Orphan Asylum (Philadelphia, Pa.)
- 48 Orphanages
- 14 Orphans
- 5 Orphans (Sculpture)
- 24 Orsay, Alfred Guillaume Gabriel, comte d’, 1801-1852
- 2 Orthodox churches
- 3 Orthodox Street
- 2 Osage
- 1 Osage Avenue
- 1 Osborn Manufacturing Co.
- 5 Osborn Street
- 2 Oscawana Corners, New York
- 8 Oscawana, New York
- 1 Osceola Mills (Cope, Thomas and William)
- 1 Ossian
- 2 Oswego, New York
- 1 Otis Brothers & Co. (New York, N.Y.)
- 2 Otsego Street
- 4 Otters
- 2 Otto Eisenlohr & Bros.
- 1 Otto Gerdau (Firm)
