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| Name | Total | Name | Total | Name | Total | Name | Total | Name | Total |
|---|
| Ost | 2 | Olmstead | 20 | Osborn | 4 | Ottarsson | 1 | Oreby, de | 2 |
| Overton | 1 | Orr | 2 | Onley | 1 | Orkney | 2 | Oxenbridge | 2 |
| Owen | 44 | Osterkamp | 9 | Omer, St. | 1 | Old | 1 | Oilly Constable of Oxford Castle, de | 1 |
| Orange | 4 | Ogan | 10 | Olney | 2 | Olaffsson | 1 | Orreby, de | 4 |
| Osborne | 8 | Odekirk | 1 | Owain | 1 | Oldham | 2 | Otto | 1 |
| Oliver | 8 | Ormsby | 3 | Osterhout | 1 | Orvis | 1 | Ormeston | 1 |
| Orcutt | 10 | Orman, Van | 1 | Ober | 1 | Orton | 1 | Oakes | 2 |
| Oldenburg | 5 | Ode | 2 | Odding | 1 | Oakley | 2 | Oldhall | 1 |
| Oldenburg of Denmark | 4 | Olive | 1 | Omanson | 1 | Olafsdottir | 1 | Orreby | 1 |
| Oddingeseles | 1 | Ogilvy | 1 | Owens | 3 | Olafsson of Sweden | 1 | Oeningen, von | 1 |
| Okehampton\ | 2 | Oglivy | 1 | Ordmaer | 2 | Obotrites, the | 1 | Oeren, von | 1 |
| Oilly, de | 1 | Opdendyck | 10 | Offley | 3 | Olafsdottir of Sweden | 1 | Osbert | 1 |
| Oswald | 3 | Onion | 1 | Orleans | 1 | Orléans, de | 2 | Ormsdotter | 1 |
| Oisy, de | 3 | Ogden | 11 | Oates | 1 | Other | 1 | Oosterhout | 1 |
| Olcott | 8 | Orchard | 2 | Otes | 1 | Olba (Alda) | 1 | Ossorio, de | 1 |
| Ottey | 1 | Odenhal | 1 | Oddingeseles, de | 1 | Ossory, of | 1 | Octavia | 1 |
| Otis | 4 | Osgood | 2 | Olafsson | 5 | Orkney, of | 1 | Ostercarius | 1 |
| Ort, Van | 1 | Oviatt | 3 | Obotrites | 1 | Odingsells, de | 4 | Ogilvie | 16 |
