| Surname | Individuals |
|---|---|
|
O'Brien
|
24 |
|
O'Connell
|
1 |
|
O'Connor
|
2 |
|
O'Donoghue
|
3 |
|
O'Haire
|
1 |
|
O'Halloran
|
1 |
|
O'Hanlon
|
1 |
|
O'Hara
|
1 |
|
O'Hare
|
1 |
|
O'Hehir
|
1 |
|
O'Malley
|
13 |
|
O'Mara
|
1 |
|
O'Meally
|
1 |
|
O'Neall
|
1 |
|
O'Neil
|
3 |
|
O'Neill
|
2 |
|
O'Reilly
|
1 |
|
ODwyer
|
2 |
|
Oakes
|
24 |
|
Oakley
|
23 |
|
Oates
|
2 |
|
Oatley
|
2 |
|
Obrien
|
1 |
|
Ocken
|
1 |
|
Odds
|
1 |
|
Oddy
|
1 |
|
Odgers
|
6 |
|
Odonoghue
|
4 |
|
Okeeffe
|
1 |
|
Olde
|
1 |
|
Oldfield
|
59 |
|
Oliver
|
8 |
|
Olson
|
2 |
|
Omara
|
1 |
|
Oram
|
11 |
|
Orchard
|
2 |
|
Oreilly
|
1 |
|
Organ
|
3 |
|
Orth
|
14 |
|
Oscar L S
|
1 |
|
Outten
|
1 |
|
Overton
|
2 |
|
Owen
|
2 |
|
Oxley
|
1 |
|
OÇonnell
|
1 |