| Surname | Individuals |
|---|---|
|
O'Brien
|
15 |
|
O'Bryan
|
8 |
|
O'Connell
|
6 |
|
O'Conner
|
1 |
|
O'Donnell
|
38 |
|
O'Dowd
|
1 |
|
O'Halloran
|
4 |
|
O'Hara
|
1 |
|
O'Heron
|
3 |
|
O'Malley
|
1 |
|
O'Mara
|
1 |
|
O'Neil
|
5 |
|
O'Neill
|
12 |
|
O'Regan
|
9 |
|
O'Riley
|
1 |
|
O'Rourke
|
1 |
|
O'Sullivan
|
2 |
|
Oakman
|
1 |
|
OâNeill
|
2 |
|
OBrien
|
3 |
|
Oehm
|
7 |
|
Offord
|
3 |
|
OHan
|
1 |
|
Ohlsen
|
1 |
|
Oke
|
2 |
|
Olde
|
1 |
|
Oldmeadow
|
1 |
|
Oldroyd
|
1 |
|
Oliphant
|
2 |
|
Olive
|
3 |
|
Oliver
|
4 |
|
Olsen
|
13 |
|
Olsson
|
24 |
|
Olumets
|
1 |
|
Omant
|
4 |
|
ONeill
|
6 |
|
Orford
|
1 |
|
Ormerod
|
1 |
|
Ormond
|
1 |
|
Orr
|
1 |
|
Osborne
|
6 |
|
Osbourne
|
1 |
|
Oswald
|
3 |
|
Outerbridge
|
1 |
|
Ouwehand
|
3 |
|
OWEN
|
1 |
|
Owens
|
1 |
|
Oxenbridge
|
1 |
|
Oxley
|
5 |