- 7 Office equipment & supplies
- 2 Office furniture
- 1 Office of War Information
- 8 Office workers
- 89 Offices
- 5 Officials
- 1 Ogasawara-gunto, Japan
- 5 Ogden Street
- 1 Ogden, John M., 1791-1882
- 1 Ogle's Mill
- 1 Oglevee, Welsh & Company (Firm)
- 10 Ogontz Avenue
- 11 Ohio
- 1 Ohio House
- 3 Ohio State Building
- 2 Oil (substance)
- 1 Oil cans
- 2 Oil dryers
- 1 Oil furnaces
- 8 Oil mills
- 3 Oil paintings (visual works)
- 1 Oil storage tanks
- 1 Oil well drilling rigs
- 5 Oilcloth
- 8 Oils and fats, Edible
- 1 Ointment jars
- 2 Okinawa, Japan
- 6 Okinawa, Japan
- 1 Okinawa, Japan
- 1 Okinawa-jima, Japan
- 1 Oklahoma
- 1 Olcott, Frances Jenkins, 1872–1963
- 1 Old Abe
- 195 Old City
- 4 Old City Hall
- 1 Old Colony Rivet Works
- 65 Old Curiosity Shop
- 1 Old Fairmount Engine Building
- 1 Old Faithful Geyser
- 3 Old Guard State Fencibles
