That deliberate reshaping of the southern tip of St. Patrick's Island, recorded by archaeologists, tells you something about how seriously this place was taken; someone went to considerable effort to make it work. The church that stands there today, roofless but largely intact, retains a groin vault over its chancel, a vaulting technique in which two barrel vaults intersect to form a self-supporting stone ceiling, which has kept the six-metre chancel covered where the longer nave, once slated or shingle-roofed, has long since lost its covering.

The island had a monastic presence long before the Normans arrived. The early foundation was associated with St. Mochonna, also known as Doconna or Conna, whose feast falls on the 13th of January. In 798, the Danes burned the monastery and broke the shrine of Dochonna, an act specific enough to suggest the shrine was a significant object rather than incidental damage. The community survived in some form, and in 1120 a priory of the Canons Regular of St. Augustine was formally established on the island, then known as Inispatrick. The Augustinian canons were a reform movement of the period, living communally under a rule rather than as independent monks. The arrangement did not last indefinitely on the island itself: in 1220, Henry of London, Archbishop of Dublin, moved the community to a more convenient location on the mainland, a place called Holm Patric, though the old name was retained for some time. The church fabric tells its own story of adaptation; at some later point, a rough wall was inserted across the nave to divide it in two, converting the western end into a basic shelter, which suggests the building remained in use informally long after any formal religious life had ended.

The church is built from the carboniferous limestone of the island, with calcareous tufa reserved for decorative stonework, including the arch of the north window and the vault stones. Tufa, a porous rock formed from calcium carbonate deposits, was often favoured for vaulting because of its relative lightness. The site is subject to a preservation order under the National Monuments Acts, and access to the island is by water. Visitors should look for the round-headed windows in the chancel walls, the small niche in the south wall, and the foundations of a narrow rectangular structure, fifteen metres long, to the south of the church.