After posting the earlier query, and furthur seaching of Scot and Irish Clan names, I can still find no reference to a McGirt Surname. I have a theory that the name came from the Old Norse given name Gjert, in which the J is silent or pronounced as Y. Mc or Mac is simply Celtic for son-of. It is also a tip-off that the earlier Gjert had been integrated into the local Celtic Community. There were eary Viking settlements in Scotland (Orkneys, Shetlands and Hebrides), as well as Ireland (Dublin), all with Celtic populations. The name Raold (as in Lord Raold McGirt) is also Nordic.I believe that te McGirts were originally Vikings who were integrated into the local Celtic population, and are either of Norse-Irish or Norse-Scot descent. Exactly which one is another question. Any comments on this theory would be welcome.