The limestone walls are densely overgrown, and the fabric of the building has been absorbing the landscape for centuries, a process that began long before anyone now living could remember. What survives is a two-part structure of nave and chancel, with a narrow bluntly pointed chancel arch dividing the two spaces, and a large burial vault inserted into the western end of the chancel at some later point, the kind of addition that speaks to generations of local families treating the ruin as something still actively theirs.

The church was already described as being in ruins in 1774, which means its collapse predates almost everything we associate with the better-known suppressions and abandonments of Irish ecclesiastical life. Its origins, however, reach much further back. A church at this location appears in the Papal Taxation of 1291, a medieval survey levied on church properties across Europe, which places Killathy within a documented ecclesiastical landscape of late thirteenth-century Ireland. The scholar Power, writing in 1932, identified Killathy with Ceall Aichedh, a subsidiary church of the Tuath O Quain, recorded in the early Irish territorial document known as Crichad an Chaoilli, a text describing the ancient divisions of what is now County Cork. That identification, if accepted, ties this overgrown ruin to a layer of Irish church history that predates the Norman presence entirely.

The walls themselves still offer something to read. The west wall stands to approximately three metres, and the east gable of the chancel reaches its full original height. A segmental arch, a shallow curved arch common in medieval construction, once covered the north doorway, though its sides have since collapsed. There is a probable window position in the south wall of the chancel, and a gap in the south wall of the nave wide enough to suggest a former doorway. The details are there for anyone patient enough to look through the overgrowth.