The church, built in 1810, sits within what was once a D-shaped enclosure roughly 40 metres across, and the two have been quietly occupying the same ground ever since. No earthwork, bank, or ditch remains visible today, yet the enclosure's outline was still legible enough on the first edition of the Ordnance Survey six-inch map to be recorded with reasonable precision.

Enclosures of this kind are common across the Irish landscape, and many date to the early medieval period, though without excavation it is rarely possible to say exactly when or why a particular one was built. What makes the Garrynagry example quietly interesting is the way it illustrates a pattern that appears repeatedly in Irish ecclesiastical geography: church sites positioned within, or directly inheriting the boundaries of, earlier enclosed spaces. Whether the church builders in 1810 were aware of the older feature, or simply chose the same elevated or well-drained patch of ground that an earlier community had favoured, is not recorded. The original Ordnance Survey mapping, carried out in the nineteenth century, captured the enclosure's D-shape before any surviving trace disappeared entirely from the surface.