The ruined structure measures some 21.6 metres long and 7.38 metres wide, and if you walk around it carefully you begin to notice the joins: an early Christian oratory, probably among the oldest fabric on the site, has been absorbed into a later medieval rebuild, its western gable and part of its southern wall still visible within the larger construction. That kind of layering, where a much earlier sacred building is not demolished but incorporated, is relatively uncommon, and it gives Kildaree a quality of compressed time that is unusual even among Irish ecclesiastical ruins.

The site is reputedly connected with St Fursey, the seventh-century Irish monk who founded a monastery here before travelling to England and eventually to Francia, where he became a significant figure in the spread of Irish monastic culture on the Continent. Whether the earliest fabric here dates from his lifetime is difficult to say with certainty, but the presence of a trabeate doorway, meaning one with a flat lintel rather than an arch, in the old western gable points to early medieval construction. The late medieval church that encloses it has its own architectural interest: a shallow pointed arch doorway in the southern wall, two twin-light windows with differing heads, one round and one ogee-shaped, and a traceried east window set slightly off-centre, which appears to have replaced an earlier opening, the southern jamb of which is still legible on the interior face. Inside, a north-south dividing wall and a small opening high in the western gable suggest the western end once held a loft. Small recesses called aumbries, used to store liturgical vessels, survive in the east gable and at the eastern end of the south wall. Beneath the curving western wall of the graveyard, traces of an older wall may mark the boundary of the original early ecclesiastical enclosure, the precinct that once defined the monastic settlement itself.

The graveyard surrounding the church is still defined by a modern wall and the ground is described as rising gently above the surrounding grassland. For anyone who knows what to look for, the off-centre east window and the visible jamb of its predecessor inside the wall repay close attention, as does the junction between the early oratory masonry and the later medieval fabric in the western end.