It is used as a first name in Ireland. I know a girl named Kerry (perhaps it's spelt with an i) who is named such because her parents are from there. (They now live in Dublin).
What I don't understand is that on this website it's an English name but it comes from an IRISH county. Surely that makes it Irish? I suppose if it was going to be Irish it'd have to be spelt Ciarrai like the county? [it's not used as a first name in Ireland -ed]
In response to Gianna's comment, where the ed said that Kerry isn't used in Ireland, I know quite a few Kerrys here in Northern Ireland. Does that not make it Irish?