1836
O Surnames
| Surname | First Name | County | Page |
| O Bryant | Dennis | Dubuque | 33 |
| O Mara | Micahel | Dubuque | 20 |
| O Neill | William | Demoine | 77 |
| Ogle | Anderson | Demoine | 87 |
| Oliver | E.E. | Dubuque | 32 |
| Ops | Lewis | Demoine | 67 |
| Orr | A.S. | Dubuque | 33 |
| Osborn | Solomon | Demoine | 52 |
| Owen | Josua | Demoine | 58 |