History Of the O'Callaghan Clan

The name of O'Callaghan, in Irish O'Ceallachain, was taken from Ceallachain, King of Munster, who reigned from Cashel in Co. Tipperary and died in 952 AD. The years following his death were riddled with killings and counter-killings as various factions fought for dominance. Eventually the McCarthy's, also descendants of Ceallachain won supremacy and became the overlords of the O'Callaghans about 1120.

The O'Callaghans became dispossessed during the Anglo-Norman invasion of Ireland and they settled in an area of County Cork about the year 1300. This area was located on the banks of the Blackwater river, about 5 miles west of the present-day town of Mallow and was known as "Pobul-I-Callaghan", the territory of the O'Callaghan clan.

They were one of four clans in the Barony (Barony is a sub-division of a County) who were subjects of the McCarthy Mor, who was the principal chieftain in the region. The clan lands were surrendered to Queen Elizabeth I in 1594 and regranted by her to the chief to be held under English law. This surrender and regrant gave rise to landmark court cases in 1594 and 1607. These cases ultimately determined that the English system of family inheritance should prevail over the Irish system of clan inheritance.

The O'Callaghans were again dispossessed during the Cromwellian regime about 1658 and the leading families transplanted to County Clare, where the village of O'Callaghan's Mills still bears their name. The humbler members of the sept were not transplanted and consequently Cork is where the name is chiefly found today.

It is noted by some historians that Callaghan is one of the names where the Irish form of the name, O'Callaghan, has been most widely resumed. About 50 years ago the "Callaghan" form outnumbered the "O'Callaghan" form by a ratio of about five to one. Today, O'Callaghan far exceeds Callaghan and between both forms the number of people with these name in Ireland today is about 13,000.

O'Callaghan is one of only about 16 families in Ireland today of which a "Chief of the Name" is recognized by the Irish Genealogical Office.