The Irish Gaelic title seems to be a recent invention (20th century, IIRC); the tune was originally named, and published (in Scotland), as Da Mihi Manum (Latin); and such stories as we have concerning its composition all agree, so far as I can tell, that it was made in Scotland; though it is also generally considered that the Blind Rory is question was the Irish harper rather than the Scottish one. Bruce Olson, I think, had useful things to say on the subject in some of the numerous other discussions here.

As usual, an enthusiastic newcomer has managed to find a very old thread which lacks the better information provided in more recent ones. I gather that O'Kane has occasionally been connected anecdotally with the Londonderry Air, but I'm not aware of any evidence that might support that claim, and would be glad to hear of any such.