I don't have any data to offer regarding your McGatlin line--only some observations gathered from years of reflecting, searching and discovering the origins of the name Gatlin.I would be interested in any data you might have acquired during your trip to Ireland.
I'm not surprised that your ancestor John McGatlin hails from Ireland. I've heard of numerous Gatlin sightings in Ireland from various Irish friends.I'veonly once directly encountered the McGatlin name, in Lewisville, TX, when I was a boy.
The name Gatlin probably derives from Gatland which refers to people who live in enclosed or gated land.The spelling Gatlin probably reflects a lazy pronunciation of the name. I speculate that Gatlands from England emigrated to Ireland during Eliabethan and Cromwellian times as well as during the reign of William and Mary in England, roughly 1560-1700. The Mc prefix was probably added to make the name sound more Irish or to indicate that this particular Gatlin was the son of another Gatlin say during the second or third generation after migration.
There is an Isle of Gatlin off the coast of Co. Kerry so I'm told.
The name Gatland seems fairly widespread in England; You find it as far north as Staffordshire in the n. midlands arcing southeastward through Nottinghamshire, Norfolk, Suffolk, into the home counties around London.It seems to be especially concentrated in Co. Sussex around the town of Cuckfield.I believe there have been Gatlands in that area since the late 1200's.
It appears that most of the southern American Gatlins are descended from John Gatland the Immigrant who came from Sussex to Nansemond and Isle of Wight Co's. VA in the mid 1630's.
Would enjoy corresponding with you if you are interested.