| Name | Census Frequency |
|---|---|
| Mary O' Neill | 40 |
| John O' Neill | 34 |
| James O' Neill | 23 |
| William O' Neill | 15 |
| Elizabeth O' Neill | 13 |
| Charles O' Neill | 12 |
| Catherine O' Neill | 11 |
| Thomas O' Neill | 10 |
| Edward O' Neill | 8 |
| Patrick O' Neill | 8 |
| Annie O' Neill | 7 |
| Henry O' Neill | 7 |
| Alice O' Neill | 6 |
| Margaret O' Neill | 6 |
| Ellen O' Neill | 5 |
| Jane O' Neill | 5 |
| Michael O' Neill | 5 |
| Ada O' Neill | 4 |
| Agnes O' Neill | 4 |
| Arthur O' Neill | 4 |
| Bridget O' Neill | 4 |
| Daniel O' Neill | 4 |
| Eliza O' Neill | 4 |
| Francis O' Neill | 4 |
| George O' Neill | 4 |
| Rank | Surname | Match | Census Frequency |
|---|---|---|---|
| 1 | O Brien | 38% | 4,889 |
| 2 | O Neill | 88% | 2,288 |
| 3 | O Connor | 13% | 2,195 |
| 4 | O Neil | 75% | 2,053 |
| 5 | O Donnell | 44% | 1,424 |
| 6 | O Hara | 25% | 1,225 |
| 7 | O Brian | 38% | 1,034 |
| 8 | O Connell | 44% | 829 |
| 9 | O' Brien | 50% | 734 |
| 10 | O Hare | 25% | 666 |
| 11 | O Leary | 38% | 566 |
| 12 | O Neal | 63% | 407 |
| 13 | O Niel | 63% | 386 |
| 14 | O Conner | 13% | 382 |
| 15 | O' Neill | 100% | 368 |
| 16 | O Sullivan | 20% | 300 |
| 17 | O Shea | 25% | 299 |
| 18 | O Malley | 25% | 296 |
| 19 | O Reilly | 63% | 286 |
| 20 | O' Connor | 33% | 277 |
| 21 | O Grady | 25% | 249 |
| 22 | O' Hara | 38% | 249 |
| 23 | O' Neil | 88% | 249 |
| 24 | O Rourke | 13% | 228 |
| 25 | O Bryan | 25% | 223 |
| 26 | O Keefe | 38% | 214 |
| 27 | O' Donnell | 60% | 206 |
| 28 | O Toole | 38% | 180 |
| 29 | O Donald | 25% | 163 |
| 30 | O Keeffe | 25% | 150 |
| 31 | O Donoghue | 20% | 140 |
| 32 | O' Brian | 50% | 130 |
| 33 | O Niell | 63% | 128 |
| 34 | O' Connell | 60% | 128 |
| 35 | O Callaghan | 18% | 123 |
| 36 | O Dell | 63% | 115 |
| 37 | O Boyle | 38% | 114 |
| 38 | O Hanlon | 25% | 111 |
| 39 | Owe | 25% | 105 |
| 40 | O' Leary | 50% | 104 |
| 41 | O Hagan | 25% | 100 |
The surname O' Neill is the 15th most popular variant of O Brien.