I'm a Mac Caolain whose ancestors were around Kilkeelan, Co. Meath (Coill Caolain) since the 16th century and my YDNA points to an East Breifne origin. I think this was part of a larger family that settled around what is today Shercock, Bailieborough, (near Crossmakeelan: Crois Mac Caolain) and was once part of Clann Chaoich an Feadha (Clan Kee of the Wood). If any McKeelan from Cavan interested and would like to participate, I'd be happy to send a YDNA test from FamilyTreeDNA to establish whether we are or related or not. It could also be these names spawned from two separate individuals named Caolain. The reason I am specifically looking for someone with a papertrail in this area is because the name O'Ceilachan in Monaghan-Louth also anglicized to Keelan as it dropped a syllable somehow.
