Around 250 metres to the south, the ground once met the original shore of Ballyteige Lough, known in the seventeenth century as Mablen Haven. The church served the parish of Ballymagir, also called Killag, and is reputedly dedicated to St Degumen, or Decuman, a Welsh saint, which points to early medieval sea-borne connections between Wales and the Wexford coast that were neither rare nor incidental in that period. The building sits within a subrectangular graveyard defined by earthen banks, entered from a north-south road by a path of about thirty metres.

What survives is a nave and chancel, ivy-covered on the side walls to roughly two and a half metres, with the east and west gables still standing complete. The west gable retains a double bellcote and a slit window, and corbels inside the nave indicate that a timber gallery once occupied its western end. A pointed granite doorway remains in the south nave wall, but a corresponding north doorway noted by the scholar John O'Donovan around 1840 has since vanished entirely. Beneath a relieving arch in the same south wall lies a wicker-centred burial vault, a construction method in which woven rods formed the centering over which the vault was built. The chancel contains a piscina, the small stone basin used for rinsing communion vessels, carved from dressed sandstone, and a series of arched tomb recesses in both walls. One of those on the north wall, flanked by pilasters, functioned as an Easter Sepulchre, a niche where the consecrated Host was reserved between Good Friday and Easter Sunday as a physical enactment of Christ's entombment and resurrection. The west end of the chancel was rebuilt in the nineteenth century as a mortuary enclosure for a family of O'Neill, breaking the earlier chancel arch in the process. Four stones identified in 2015 appear to be fragments of a single wall memorial: an armorial stone dated 1637 carries two heraldic crests, one clearly associated with the Walsh family, the other combining elements linked to the Whitty and Deveraux families, with the initials I W carved above it. A fourth fragment shows carved symbols of the Passion, among them a ladder, pincers, dice, and the seamless robe, details drawn from the Gospel accounts of the crucifixion and common in late medieval devotional carving.