Through his father Sétna, Mainchín is alleged to belong to the Dál Cais, given a pedigree linking him to the ancestors of the O'Brien dynasty.
[1] Mainchín is said to have founded Luimneach when Ferdomnach, king from the Dál Cais, granted him land at Inis Sibtond.
A major problem with the above is that the Dál Cais themselves are unknown by that name before the 930s and are believed by scholars to be the descendants of a Déisi population which migrated into the region at an uncertain period.
It has been argued that his appearance in Limerick is actually due to his adoption by the later Norse there, with whom the O'Donovan family, late representatives of the kingdom (although of uncertain origins themselves), were closely associated.
In Bruree, his feast day is commemorated on 2 January, but this date may have been erroneously taken from that recorded for St Manchán (Manchéne) of Min Droichit in the Félire Óengusso.