This surname means descendent of Ceallach?n who was the E?ganachta King of Munster from AD 935 until 954. The personal name Cellach means 'bright-headed'. The principal sept of the name Callaghan were lords of Cine?l Aodha in South Cork originally. This area is west of Mallow along the Blackwater river valley. The family were dispossessed of their ancestral home and 24,000 acres (97 km2) by the Cromwellian Plantation and settled in East Clare.