The project is open to all O'Callaghan, Callaghan & Callahan, Keelaghan, Kelaghan males, (and variants) from Ireland, especially Counties Cork, Mayo, Tipperary and Clare. Munster The surname means descendent of Ceallachán who was the Eóganachta King of Munster from AD 935 until 954. The personal name Cellach means ‘bright-headed’. The Callaghan lands were traditionally west of Mallow, Cork along both sides of the Blackwater river valley, comprising the parishes of Kilshannig and Clonmeen. The Callaghan’s were dispossessed of their ancestral home of approximately 50,000.00 acres during the Cromwellian Plantation and settled in East Clare. Oriel Ó Ceileacháin in Irish, is to be found in the counties Armagh, Louth, Meath and Monaghan. It has been anglicized as Callaghan, Kelaghan, Keelaghan, Kealahan and other variants. In County Meath, where it is widespread but has been found mainly in the parishes of Kells, Trim and Athboy, it is mainly anglicized as Callahan, Callaghan or O'Callaghan (with local spelling variants). In County Westmeath it is still found in the form Kelaghan. In County Monaghan it is often found as Keelan. Members of the Ó Ceileacháin family were mentioned in the Annals of the Four Masters as being lords of Uí Breasail, a district on the southern shore of Lough Neagh, and priors ofArmagh in the 11th century. Mayo/Sligo/Donegal There is also a Mayo family of this name, a branch of the Ui Fiachach, who were anciently the lords of Erris. See Patrick Woulfe, Irish Names and Surnames (1923).