- 2 Old man
- 2 Old Man's Home of Philadelphia
- 1 Old Oaks Cemetery
- 3 Old Plough Tavern
- 2 Old Point Comfort, Virginia
- 1 Old style (typeface group)
- 16 Old United States Mint
- 1 Old York Road
- 11 Old York Road
- 3 Old York Road
- 1 Old York Road
- 1 Old York Road
- 1 Oldach & Co. Bookbinding
- 3 Olive branches
- 1 Oliver Farm Equipment Company
- 35 Oliver Twist
- 1 Olives
- 4 Ollier, Charles, 1788-1859
- 1 Ollier, Edmund, 1827-1886
- 2 Olliffe, Laura Cubitt
- 5 Olliffe, Sir Joseph (1808-1869)
- 1 Olney
- 28 Olney
- 7 Olney Avenue
- 1 Olney, Pennsylvania
- 4 Olympic Theatre (London, England)
- 1 Ombos, Egypt
- 1 Omnibus Co.
- 32 Omnibuses
- 3 Once I was rich (Sculpture)
- 1 Ondatra zibethicus (species)
- 1 Oneida Steam-engine & Foundry Co.
- 2 Ontario
- 11 Ontario Street
- 9 Openings (events)
- 28 Opera houses
- 4 Opera singers
- 4 Operas & operettas
- 5 Operas (performances)
- 2 Operators
