Trinity Island is the site of one of two religious foundations on Lough Key.
The ranks of Canons were augmented in 1228 by the defection of monks from the Cistercian Abbey of Boyle, which was seen by the Cistercian Council of that year as having become too gaelicized. The monks brought with them their manuscripts and learning, which, under Clarus’ direction, developed eventually into the great manuscripts of the Annals of Lough Key and the Annals of Connacht.
A text in latin records a dispute between the Canons here, and the Monks of Boyle, over the burial of Dermot Mac Gilla Carraig, erenach of Tibohine, in 1229.
The monastery was granted protection by the Justiciar of Connacht, when he and other Anglo-Norman notables visited it to pray, prior to attacking MacDermot’s castle in 1235.
After the general suppression of the monasteries by Henry VIII in 1536-7, this monastery was granted to the Mac Dermots who allowed the Canons to remain in occupation, and it appears that they continued to occupy the House until it was confiscated by James I in 1608 The Island is the burial place of Sir Conyers Clifford, the Commander of the English forces in the Battle of the Curlews, 1599.