There are 48 unique father surnames beginning with O:

O'Brian	O'Brien	O'Conner	O'Connor	O'Dea	O'Donnell	O'Hara
O'Harra	Obedier	Oberdier	Oday	Odea	Odell	Oehler
Ogan	Ogle	Oglesby	Ohaver	Ohler	Oldoerp	Olds
Oliphant	Olive	Oliver	Oller	Omeroid	Ophile	Opphile
Oppihle	Orahood	Oram	Orange	Organ	Ormeroid	Orr
Orrison	Osbern	Osborn	Osborne	Otte	Ottee	Ottie
Ousler	Overacker	Overfield	Overholster	Overturl	Owen

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