Most of the building has gone, or nearly so: three walls survive only as foundations and scattered lower courses, their stones long since carried off for other purposes. Only the south wall still reads as a wall, rising to between 2.2 and 3.9 metres in places, its rubble core exposed where the facing has fallen away. What remains is enough to suggest a building of some ambition. The antiquarian Thomas Johnson Westropp, writing around the turn of the twentieth century, noted the masonry as being of unusual size, the stones larger than one would typically expect in a structure of this kind.

The church, recorded under the older spelling Knocknanangel, is a single-cell building, meaning one undivided rectangular room, measuring just over fourteen and a half metres internally from east to west and just under five metres north to south. Its south wall contained two doorways and a window embrasure between them, though the window itself has been robbed out entirely. The wider of the two southern doorways, at 1.25 metres, has been reduced to its foundations; the narrower eastern one, at 0.8 metres, retains its straight ingoings, the vertical sides of the opening. The north wall once held a centrally placed doorway 1.3 metres wide. Cairn material outside the south wall may represent the collapsed remains of a structure once attached to the eastern doorway, though no coherent ground plan can be made out. Westropp also noted a grass-covered platform to the north, defined by low scarps, which may have been a related building. The church lies roughly 200 metres south-west of the island's cathedral, placing it within what was clearly a substantial monastic complex on this small tidal island in the Shannon estuary.