Surnames A-Z Surnames Registered with the Guild Each of the surnames listed is the subject of a one-name study carried out by a Guild member and links to our full search results for that study. If the results include a study profile, the link is shown with a light grey background. Select an initial letter to view our list of registered surnames:A B C D E F G H I J K L M N O P Q R S T U V W X Y Z We have 97 registered surnames beginning with O. O'Callaghan O'Donnchadha O'Donoghue O'Donohoe O'Donohue O'Donoughue O'Farell O'Farrall O'Farrel O'Farrell O'Fearghail O'Hara O'Harrow O'Kennedy O'Laoghaire O'Laohaire O'Laoire O'Leary O'Mara O'Meara O'Muireagr O'Raighne Oaldham Oatway Obank Oberry Obray Obree Obrey Odom Ogborn Ogborne Ogbourne Ogburn Okeborne Olby Oldacre Oldacres Oldaker Oldakers Oldam Oldbury Oldham Oldom Oldum Olford Olstead Omara Orange Orenge Orgar Oringe Orlanda Orlande Orlando Orrange Orrett Orringe Orritt Orwick Orwin Orynge Ossic Osterbery Osurck Oswic Oswick Otar Oter Ottar Otten Otter Otton Otway Ouston Ouvry Ovard Ovenstede Over Overd Overs Overy Ownstead Owstaby Owston Owston-Doyle Oxlad Oxlade Oxland Oxlar Oxlard Oxlat Oxlede Oxlet Oxlord Oxwick O’Hallinan Select an initial letter to view our list of registered surnames:A B C D E F G H I J K L M N O P Q R S T U V W X Y Z