Drennan was orginally spelt O' Draighneain ( draighnean means
blackthorn). It is usually accepted that the sept of of O'Drennan
belonged to the Siol Anmchadha group, located in Longford, Co.
Galway. The Four Masters record the death of Gillachiarain
O'Draighnen in 1163 in the county Westment. Other families
were living in Leinster counties and the county Tipperary. Some
associate the O'Drennan name with the Thorntons. According to the
book More Irish Families "Drennan, Dreinan, Drinane, Drinan and
Meenagh were interchangeable with Thornton in the counties
Galway and Mayo, where at the present time Thornton is fairly
numerous and Drennan etc., are not." Keating History states that
O'Drennan was the chief of Slieve Eise Finn and Kinel Sedna,
which borders Galaway and Clare. "The lands aboutthe fair Slieve
Eise, are possed by the Clan Sedna of melodious barbs, A tribe who
firmly support their clans; Chief of their territory is O'Drennan."
In the 1890 birth index the Drennan family was numerous in Antrim
and Tipperary counties.
