Canon William Carrigan suggested "an ancient Church stood on the site from time immemorial to after the Cromwellian era".

[1] John O'Hanlon reported that Diocese of Ossory ecclesiastical records names Saint Manchan as patron saint writing "at Inisnag, diocese of Ossory, St. Manchan, whose feast occurs on the 14th of February, was venerated as a patron (Statuta Dioecesis Ossoriensis)".

[1] The Annals of the Four Masters has an entry for AD745, recalling the "battle of Inis Snaig", between "Anmchaidh mac Cucearca", king of Osraighe, and an unknown opponent,[3] and an entry for AD 889, "the death of "Suadhbhar mac Coitceadhach, of Inis Snaig, died an anchorite",[4] confirming the early Christian Irish monastery of Inis Snaig flourished in at least the ninth century, but probably from the early Middle Ages to sometime before, or after, the Norman invasion of the 12th century.

This Diocesan Chapter, consisted of a Dean, Archdeacon, Chancellor, precentor and Treasurer, is traceable back to Felix O'Dulaney (1178–1202), the late 12th century onwards.

James Graves once holding a correct transcript of same, the prebend of Inisnag was granted on "the authority of Pope Nicholas IV, 1291 [liber ruber Ossoriensis]".