A notable feature of the distribution of Irish surnames throughout the Island of Ireland, is often the attachment of certain surnames to particular areas, often for many centuries. This can be seen in the distribution of Irish families even today in the early twentyfirst century.
Historically in Gaelic Ireland, families retained their surnames over the centuries unchanged. The O'Donnell or O'Neill lords of Tír Chonaill and Tyrone were still called O'Donnells and O'Neills four centuries later. Occasionally surnames changed slightly or were confused such as the manner in how the McLoughlin family of Tyrone are sometimes recorded as O'Loughlins in some sources. From time to time a branch of a major surname could also sometimes adopt a unique surname for a period, such as the McShanes, the sons of Shane O'Neill, the lord of Tyrone who was killed in 1567, did in the latter years of the sixteenth century.