The round-headed ope, rising from ground level to a height of 3.5 metres and spanning 2 metres across, is formed from long, narrow voussoirs, the wedge-shaped stones that lock an arch together, and its proportions suggest it may originally have been intended as an archway leading into a chancel. No trace of that chancel survives above ground. The church itself is a modest rectangular structure, roughly 12.7 metres east to west and 6.7 metres north to south, with the side walls still standing close to their full height while the gables have lost their tops and edges. A second round-headed doorway in the west wall, at just over two metres high and a little over a metre wide, has a plain limestone surround with a slightly enlarged keystone and block capitals, giving it the appearance of late seventeenth-century workmanship.

The church's last period of active use left a reasonably detailed paper trail. A description from 1700, cited by Lunham in 1909, records it as being in good repair, furnished with seats and a pulpit, the communion table railed in and the interior walls plastered. The same account credits the father of a Captain St. Leger with having the building repaired around 1680, the cost met through a presentment at the assizes, a legal mechanism by which grand juries could levy local funds for public works. Despite that relatively recent intervention, the core of the structure is likely older. By 1837 the church had fallen out of use as Rathcooney's parish church, and it has been a ruin ever since, sitting at the centre of the graveyard that surrounds it, as recorded on the Ordnance Survey six-inch map of 1842.