The apostrophe in O'Hara does not mean son of O'Hara, but *grandson* of
O'Hara.
Nowadays it is often used as "Of" the O'Haras.
My name is McCormick and I am descended from Laurence O'Hara (b 1770 in
Co. Sligo, but moved to Co. Roscommon). He married Mary McDonagh and I
have hundreds of their descendants listed on my tree at Ancestry.co.uk.
If you are a member of Ancestry you can view my tree for free. "The
McCormick (Niall) Family Tree"
If you have any information that would help with the expansion of my
tree, I would be really pleased to hear from you,