The site is unusual not just for its age but for how much it preserves and how much it has quietly lost: a triple-light tracery window in the east gable still stands to its original height, four slender lancet windows survive almost intact in the south wall of the church, and a medieval graveslab rests inside on four dumb-bell piers salvaged from the cloister arcade. Yet the great gateway noted by late eighteenth-century visitor Daniel Grose is gone entirely, as is the stone cross that once faced it, and the lofty belfry he recorded near the transept had already fallen by the time he arrived to paint the place.

The island's religious history may begin as early as the sixth century, with a monastery possibly founded by St Ciarán before 542. The Augustinian priory, a community of canons regular living under the Rule of St Augustine, was built around 1259, and the fabric of the church reflects two distinct campaigns of work: the diagonal stone-tooling on the lancet window jambs points to thirteenth-century construction, while the switchline tracery of the east gable window and the transept tracery both date to a fifteenth-century rebuilding. By 1552, following the dissolution of the monasteries, Richard Nugent was granted a lease of what documents called the 'monastery of canons of the Hooly Iland', described at the time as being covered with shingles; the lease was extended again in 1565. When Grose visited in the late eighteenth century, two barrel-vaulted chambers of the west range were still standing, a porter's lodge remained partially upright with a diamond-shaped chimney stack suggesting seventeenth-century adaptation, and the precinct wall, which once rose to a considerable height, still enclosed much of the complex.

What survives today includes the church walls, the lower portions of the west range, fragments of the precinct wall on the west and south-west, and a small garderobe tower, a privy chamber projecting from the outer wall, that has been heavily restored. Architectural fragments from the cloister arcade lie scattered among the graveyard memorials. A section of a long rectangular building in the north-north-west of the enclosure is largely overgrown, and wall-footings in several areas hint at the fuller plan of what was once, as Grose observed, a complex that 'must have covered a great space of ground'.