The building gave its name to the parish of Kilmacshalgan, a detail that hints at just how central this place once was to the surrounding community. What looks at first glance like a straightforward ruin turns out to be a structure that changed hands, changed faith, and outlasted several of the forces that shaped it.

The church's origins are tied to a friary established here in the thirteenth century. The friars continued to use the site through the medieval period and into the early modern era, until they were expelled during the Cromwellian campaigns of the mid-seventeenth century. By 1615, the building had already been 'repaired', suggesting it had fallen into some disrepair before being pressed into service as a Protestant place of worship, a fate shared by many former Catholic ecclesiastical sites in Ireland during this period. It continued in that function until 1812, after which it was left to decline. The walls, built of mortared limestone and ranging from 0.65 to 1 metre thick, are rectangular in plan and measure roughly 18 metres in length by just over 7.5 metres in width. The most striking surviving feature is a tall rounded-headed window in the east wall, standing approximately 3 metres high, which is the kind of narrow, arched opening associated with late medieval ecclesiastical architecture. The north wall once held three large rectangular windows topped with low arches of voussoirs, wedge-shaped stones arranged to form a curve, though all three are now blocked up. On the west wall, a recently renovated arched doorway retains a drawbar socket on its south side, the recess into which a heavy timber bar would once have been slid to secure the door from within.

The church sits within a graveyard that remains in use, and the building itself is heavily overgrown. The tall east window is the clearest indication of what the structure once was, visible above the vegetation if you approach from the right angle.