It could be asserted with truth that St. Senan's island never quite recovered as a monastic settlement after the first onslaughts of the Danes. To understand its subsequent history it must be noted that the system of church administration in Ireland for centuries after St. Patrick was almost entirely monastic in character.

Since the incursions of the Danes had been directed chiefly against the monasteries through a period of two hundred years, one can understand how grievous was the disorder that resulted to civil and religious life.

Iniscathaigh may be taken as an example. Here, from the days of St. Senan, the community of monks laboured to instruct the people of the neighbouring districts and to minister to their spiritual needs. They had established little ‘pocket-parishes’, not only in Corcabhaiscinn but along the southern side of the River Shannon.

When the foreigners invaded and occupied the island, and later set up a base of operations in Luimneach island, (later Limerick), all the surrounding districts suffered in their raids. Considering that this was the fate of very many other monasteries, it was surely providential that bishops and priests survived. Yet, they did manage to survive: and history tells us how they held many meetings and synods notably those of Rathbreasail and Kells, in an endeavour to repair the great damage that the church had suffered. The outcome of these synodal meetings of bishops and clergy was the formation of dioceses and the appointing of bishops to rule them.

The monastery of Iniscathaigh was deeply affected by the changes that ensued. The newly-formed diocese of Killaloe became co-extensive with the territory of Thomond. Included in this diocese was the island-bishopric of Iniscathaigh. But then a problem had to be solved; for the monastery had rights, interests and claims quite outside the newly formed diocese of Killaloe, namely in the dioceses of Limerick and Ardfert. This problem was solved in a rather unusual way. Twelve priests of the diocese of Killaloe were appointed to minister in those places on the north side of the Shannon, which had been previously served by the monks of Iniscathaigh. Similarly, twelve others from the dioceses of Limerick and Ardfert to serve the districts on the south side of the Shannon, where the monastery had certain rights and claims.

These 24 priests would reside in a collegiate church within the island, under the direction of a prior. Thus, it was hoped, a link with the previous monastery would be retained, while the revenues and ‘dues’ from the monastic lands (or ‘termons’, as they were called) would help to maintain these priests in their collegiate church. The priests of the diocese of Killaloe occupied the Northern half of the island which was nearer to Corcabaiscinn, while the other twelve occupied the southern half, on which stood the Church of the Hill of the Angels.

Early in the 15^th century this collegiate church was raised to the dignity of a ‘Collegiate Church Major’, with canons and chapter. However, in that same century, the priests residing in the ‘southern hemisphere’ left the island and took up residence in Ardfert.

This collegiate church with its canons occupied the island for three hundred and seventy years. It probably came into being after the death of the last bishop of Iniscathaigh, Aodh O Beachain in 1188, for it was then, in accordance with the decree of the Synod of Kells, the bishopric of Iniscathaigh ceased to exist.

Very little of the history of this institute seems to have been recorded, excepting certain papal mandates from the Holy See. The predecessors of the Canons of the Collegiate Church, the monks of Iniscathaigh, had laboured in various districts from the Fergus to Ceann Leime. Such places as Clondegad, Knock, Killimer, Mullocha, Kilrush, Monmore, Kilmacduane, Killnaceallaich, Kilfearagh, Kilcredane, Kilballyone and Ross as well as Kilmihil and Killard are mentioned in various records as having been associated with Iniscathaigh. It is very unlikely that the Canons of the island church could have served all these places in a newly formed diocese and in newly formed parishes.

The same could be stated regarding the districts on the other side of the Shannon with which Iniscathaigh was associated; Knockpatrick, Shanoway, Shanagolden, Kilsenan, Duncaha, Ballyhoolahan, and Kilnaghten.