| 21. | Ontario, Lake (N.Y. and Ont.) (1) |
| 22. | Ontario. Parliament (1) |
| 23. | Opera (1) |
| 24. | Opera companies (3) |
| 25. | Oral reading (1) |
| 26. | Ordnance (6) |
| 27. | O'Reilly, James, 1823-1875 (2) |
| 28. | O'Reilly, M. (1) |
| 29. | Orford, Mount (Quebec) (1) |
| 30. | Organ grinders (1) |
| 31. | Organ (Musical instrument) (1) |
| 32. | Organs (1) |
| 33. | Orléans, Île d' (Quebec) (1) |
| 34. | Orleans (Ont.) (1) |
| 35. | Orontes (Steamship) (2) |
| 36. | Orphanages (4) |
| 37. | Orphans (1) |
| 38. | Osgoode Hall Law School (1) |
| 39. | Oshawa (Ont.) (2) |
| 40. | Ottawa, (Ont.) (1) |