Americans tend to think of most Irish surnames as beginning with Mc or O’ and while that’s an exaggeration, it has some basis in the truth. Out of just under 300 pages of listings in the Cork phonebook, there are 56 pages of names beginning with O (and almost all of those are O’Something) and about 16 pages of names beginning with Mc (or sometimes Mac, which is the original unabbreviated form, but which is less common with Irish names today).

An Irish Times article claims that all Gaelic surnames actually do begin with either an O or a Mac, but this isn’t entirely true. An excerpt from Eugene O’Growney‘s 1898 book The Irish Ecclesiastical Record, Volume III, which appears on the Library Ireland website, explains that Ni indicates “daughter,” and was historically used by women. To provide a modern example, the Gaelic (or Irish) name of the new-age singer Enya is Eithne Ni Bhraonáin.

The Irish Times article does provide a nice explanation of how surnames originated in Ireland, pointing out that “up to the tenth century, surnames in Ireland were not hereditary,” but each generation would have a new last name. The Mc or Mac signifies “son of” in a name, and the O at the beginning of names does not mean “of” as is sometimes thought (in fact Irish names almost never indicate where a person is from), but rather “grandson of.” So, a man’s last name would reflect the given name of his father or grandfather, depending on who was more prominent. For example, Cormac O’Sullivan simply meant “Cormac, grandson of Sullivan,” and his son might be known as Brendan McCormac. Surnames eventually became fixed in the eleventh century.

Over time, though, Irish names usually became more Anglicized, and the O or Mc was usually dropped. To take one example, and show some of the variations on the name and how prevalent each variation is, O’Súilleabháin (17 listings in the Cork phone book, with some variation on where the fadas appear) became O‘Suilleabhan (one listing), and even Osuillivan (one listing). The Anglicized versions of these names became O’Sullivan (almost 9 pages, or about 3% of the total listings in the phone book), and Sullivan (about half a page of listings). There are no listings for Súilleabháin without the O‘, which I suppose reflects the idea that a person who keeps the traditional Irish spelling would keep the entire Irish spelling, and be less likely to drop the O‘.

(As an aside, on my mother’s side I’m a Sullivan, as well as an O’Connell and Crowley. My dad’s Irish lineage is harder to trace, since his grandfather was apparently born in Ireland with the decidedly un-Irish name John London.)

Names that are not originally Irish in origin but may now seem Irish to many of us don’t begin with O’ or Mac. Fitz, for example, that other piece of many Irish surnames such as Fitzgerald or Fitzpatrick, also means “son of” but is a bastardization of fils, or “son” in French, and a relic of the Norman invasion of Ireland.