| Families |
Ethnic Group |
Branch of |
| Nolan |
|
O'Houlihan |
| Nolan |
IVL - Fermanagh, Kerry |
|
| Norman |
|
MacLeod |
| Norman |
IVL - Meath |
|
| Nugent |
IVL - Meath, Cavan |
|
| Nugent |
Normans |
|
| O'Aherne |
Erainn |
|
| O'Beirne |
Gaels |
|
| O'Beirne |
IVL - Mayo |
|
| O'Beolain, O'Bolan |
Gaels |
|
| O'Boylan |
Laigin |
|
| O'Boyle |
Gaels |
|
| O'Branigan, Brangan |
Gaels |
|
| O'Brennan, Brennan |
Laigin |
|
| O'Brennan |
Erainn |
|
| O'Brennan |
Gaels |
|
| O'Brennan |
IVL - Galway, Kerry |
|
| O'Brennigan |
|
O'Branagan |
| O'Brien |
Erainn |
|
| O'Brien |
IVL - Connacht, Leinster |
|
| O'Brolachain (Argyle) |
|
O'Brollaghan |
| O'Brolan |
Gaels |
|
| O'Brollaghan |
Gaels |
|
| O'Byrne |
|
O'Beirne |
| O'Bryne |
Laigin |
|
| O'Cahan |
Gaels |
|
| O'Caherney |
|
Fox |
| O'Cahill |
Erainn |
|
| O'Cahill |
IVL - Galway, Kerry |
|
| O'Callaghan |
Gaels |
|
| O'Callaghan |
IVL - Mayo |
|
| O'Cannon, O'Canannain |
Gaels |
O'Donnell |
| O'Cannon |
IVL - Galway |
|
| O'Carroll |
IVL - Ireland |
|
| O'Carroll |
Laigin |
|
| O'Carroll |
|
MacBrady |
| O'Carry |
Gaels |
|
| O'Casey |
IVL - Limerick, Cork |
|
| O'Casey |
Laigin |
|
| O'Cassidy |
Laigin |
|
| O'Cleary |
Gaels |
|
| O'Coffey |
Erainn |
|
| O'Coghlan |
IVL - Cork |
|
| O'Colgan |
|
MacColgan |
| O'Colgan |
IVL - Derry |
|
| O'Conacannon |
Laigin |
|
| O'Connell |
Erainn |
|
| O'Connell |
IVL - Gallway, Derry |
|
| O'Connor |
Erainn |
|
| O'Connor |
Gaels |
|
|
