One of most asked questions about the McCains is their Scottish clan connections. We do actually have some. Most books on Scottish clans focus on the larger well known clans and branches of those clans. The McCain story is more complex and we are rarely mentioned in popular histories of the Highlands. Analysis of the DNA results for the family and the primary sources in Kilmichael Glassary parish connect the McCains to Clann Lachlainn. Clann Lachlainn (surname form Mac Lachlainn) was well established clan in Cowal which is across Loch Fyne from Kilmichael Glassary. Clann Lachlainn held lands in Kilmichael Glassary since the 1200s, but the McCain connection begins in AD 1436 when Ailean Mac Eáin Riabhach was granted extensive lands in Glassary. It was his son Donnchadh Rua Mac Eáin that first started using Mac Eáin as a surname. In the records of Glassary there is an ebb and flow of grants and re-grants of lands to this family by the Taoiseach of Clann Lachlainn.
So, we know that from 1436 well into the 1700s the family considered themselves a branch of Clann Lachlainn. It is more complex than that also, two Houses started by the sons of Ailean Mac Eáin were in effect employed by and closely associated with Clann Chaimbeul. So while the McCains were granted their lands via Clann Lachlainn, some of them had allegiance to Clann Chaimbeul, specifically the Earls of Argyll. We know those McCains that migrated to Ireland are linked the fifth Earl of Argyll, Giolla Easpuig Donn Caimbeul. He sent over a thousand men from Glassary to Portlough precinct in east Donegal, in the Lagan district, starting in 1569. We know that the McCains were serving as captains and bailiffs for the Earl, so the reason the family relocated to Donegal is obvious.