O
- organizations (124)
- organs (1)
- Orphan Asylum ()
- Orphan's Home Chapel ()
- Orphanages (9)
- orphanages (9)
- Orphanage ()
- orphans (3)
- Orth Congr Church ()
- Orthodox churches (11)
- Outbuildings (276)
- outbuildings (276)
- Outbuilding ()
- Outdoor Recreation ()
- Outfall sewers (4)
- outfall sewers (4)
- Outhouse ()
- Outlet Structure ()
- outside end chimneys (3)
- ovens (10)
- Overhead Loader ()
- Overpasses (11)
- overpasses (11)
- Overpass ()
- Overseer's House ()
- Owner's Cabin ()
- Ox Mill ()
- Oyster Dredging ()