| O'Connor, Doris | 83 Books | 16 Series |
| O'Dare, Deirdre | 95 Books | 2 Series |
| O'Gara, Rayne | 17 Books | 2 Series |
| O'Malley, Tierney | 17 Books | 2 Series |
| O'Quinn, Erin | 54 Books | 9 Series |
| O'Reilly, Terry | 64 Books | 1 Series |
| Obayani, Kambon | 12 Books | 1 Series |
| Oliver, Amelia | 13 Books | 2 Series |
| Olivia, R.M. | 7 Books | 1 Series |
| Olsen, Xya | 14 Books | 2 Series |
| Olson, Jodi | 53 Books | 1 Series |
| Otto, Jay | 12 Books | 2 Series |
| Owen, Chris; Payne, Jodi | 6 Books | 1 Series |
| Owens, Lisa M. | 6 Books | 3 Series |