He is often called St. Kieran the Younger to distinguish him from St. Kieran of Saighir. His feast day is September 9.
An early Irish bishop is also called Ciarán Saighir (the Elder) to distinguish him from Saint Ciarán of Clonmacnoise. Clear Island is regarded as Ciarán's birthplace. Kieran, rather than Brigid, seems to have been the pioneer founder of Irish women's convents. Around these foundations arose a village called Saigher, after the monastery. The saint is generally believed to be one of four bishops to have preceded Saint Patrick. (See also Saints Ailbhe, Declan, and Ibar.) His feast day is March 5. The coming of Christianity to Ossory is associated with St. Kieran of Saighir, the "first-born of the saints of Ireland" (Promogenitus Sanctorum Hiberniae). His foundation at Saighir Kieran flourished for many centuries. Not far distant in Aghaboe, St. Canice founded a monastery in the 6th century which grew in importance, giving Feargal to the church of Salzburg and eventually becoming for a time the site of the bishop's see. One story involves the Christmas communion of St. Cuach, Abbess of a monastery far away from Saigher. But nobody could figure out how he got to the convent of Ross-Bennchuir, so many miles distant, and returned that same night. The chronicler of the story suggests that it was by a miracle like that in which God once lifted up the prophet Habakkuk by the hair of his head and sped him from Palestine to Chaldea.
St. Carthage founded his monastery of Rahan about 590, and soon had hundred of disciples. He was consecrated Abbot-Bishop of the Fercal district, and composed a rule for his monks, an Irish metrical poem of 580 lines, divided into nine separate sections -- one of the most interesting literary relics of the early Irish Church. Numerous miracles are also recorded to him. At length, Blathmaic, a Meathian prince, instigated by the neighbouring monks, ordered St. Carthage to leave Rahan. This expulsion of the saint and eight hundred of his community took place at Eastertide of the yeare 635. Journeying by Saigher, Roscrea, Cashel, and Ardfinnan, St. Carthage at length came to the banks of the River Blackwater, where he was given a foundation by the Prince of the Decies, and thus sprang up the episcopal city of Lios-mor, or Lismore, County Waterford.
The diocese of Ossory, "Ireland's oldest bishopric", was probably co-terminus with the ancient kingdom of Ossory. Its present boundaries were set at the synod of Rathbreasail. It includes most of the county of Kilkenny (except for the parishes of Graiguenamangh and Paulstown), part of Co. Laois and the “island” parish of Seir Kieran in Co. Offaly. For a time in the 13th century its boundaries extended as far as the Barrow and included Graiguenamanagh. Already before the arrival of the Anglo-Normans the winds of change had been blowing from Continental Europe. The coming of the Cistercians to Jerpoint probably around 1160 and to Kilkenny had already signaled the passing of the old Celtic order, and soon the Canons Regular of St. Augustine were firmly installed in Saighir Kieran and Fertagh and had set up new foundations in Aghmacart, St. John's, Kilkenny, Kells and Inistioge; their sisters were in the nunnery of Kilculiheen.
The transfer of the Cathedral from Aghaboe to Kilkenny in the last decade of the twelfth century, the foundation of a cathedral chapter and the establishment of a parish system through the system of tithes introduced by the Anglo-Normans radically transformed the ecclesiastical organization of the diocese. More than half of the new parishes were in the hands of the religious, while the rest were run by the secular clergy - mostly the dean and chapter of St. Canice's. A few were in the hands of lay patrons. In the 13th century the Dominicans came to Aghaboe, the Black Abbey in Kilkenny and Rosbercon. Because of their importance in the diocese the suppression of the monasteries in the wake of the reformation led to enormous changes.
For his residence, St. Kieran (Ciaran) of Saighir built himself a cell in a place encompassed with woods, near the water of Fuaran, which soon grew into a numerous monastery. A town was afterwards built there called Saigar, now from the saint Sier-keran. Here he converted to the faith his family, and whole clan, which was that of the Osraigs, with many others. Having given the religious veil to his mother, whose name was Liadan, he appointed her a cell or monastery near his own, called by the Irish Ceall Lidain. In his old age, being desirous to prepare himself for his passage to eternity in close retirement, he passed into Cornwall, where he led an eremitical life, near the Severn sea, fifteen miles from Padstow.