In searching out the Mcdermott name in Ireland, the first choice would be in the area of Roscommon. It is believed to have originated there, other choices would be Co Mayo,Co.Donegal or other places in the North of Ireland,especially Northwest. Our MCDERMOTTs came from Co Donegal. Their emigration took place abt 1855, about 5 years after the potato famine 1845-1850. Settled in Port Glasgow,Scotland and moved on the States in 1880 and settled in Port Perry, Allegheny County, Pa. Check out the McDermott Clan Homepage on the net.
I am searching out my relatives of Butler County: Jacob Veith b. 1847 and Margaretha Osche b. 1841 both came from Alsace Lorraine
Good luck in your searches.