The graveyard at Kilmahon sits in quiet use, its memorials spanning the nineteenth to the twenty-first centuries, but its shape tells a much older story. The enclosure is roughly subcircular, measuring approximately 70 metres north to south and 62 metres east to west, and that curving outline is significant. Subcircular enclosures of this kind are strongly associated with early Irish ecclesiastical foundations, where a roughly circular boundary, known as an ecclesiastical enclosure, defined the sacred precinct around a church or monastery.

The stone wall that still runs from the north-north-east around to the north-north-west may follow, at least in part, the line of just such an original boundary. The site is thought to be connected to an early monastery nearby, and the curvature of the surviving wall lends that association some physical weight. At some point a modern concrete block wall was built cutting across the northern sector, effectively slicing off a portion of the older enclosure, and that severed area is now given over to car parking. The main entrance is through a wide wrought-iron gate in the north wall, a practical modern addition that sits somewhat incongruously against the much older logic of the space it opens into.