There are 29 unique surnames beginning with O:

O'Bryan	O'Day	O'Dell	O'Donnell	O'Haver	O'Mara	O'Neil
O.W.	Odell	Odensoff	Ogan	Ogle	Oglesby	Oldoerp
Oliphant	Olive	Oliver	Opphile	Orahood	Organ	Orr
Orris	Osborn	Osbourn	Osgoodby	Otte	Overfield	Owen
Owens

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