The ruin itself is smothered in ivy, the west gable still standing to its full height, the north wall intact to roughly three metres along its full length. Two doorways face each other across the interior, one in the north wall and one in the south, both fitted with draw-bar holes, suggesting they were secured from within. It is a compact, single-cell building, roughly 12.9 metres by 7.3 metres, with no division into nave and chancel. The place has been described as desolate since at least 1857, and the word still fits.

The name Aderrig derives from Áth Deirg, meaning Red Ford, and the church here has documentary roots going back to between 1212 and 1228, when it appears in records as the Ecclesia de Adderke. Following the Anglo-Norman Conquest, it was confirmed to the Archbishop of Dublin and later granted to St. Patrick's Cathedral. Early in the thirteenth century, Archbishop Luke directed that five marks from the church's annual income should go towards lighting the altar of the Blessed Virgin Mary in the cathedral, with the remainder distributed among the Vicars celebrating Mass there. By 1306 it had been made a prebend, a type of endowment attaching a portion of cathedral income to a particular church, and was valued at 114 shillings, with one Adam de Stratton serving as its prebendary. In 1533 it was listed among the churches of the medieval Deanery of Taney in the Reportorium Viride of Archbishop John Alen. By 1547, a twenty-one year lease including the rectory of Aderrig had passed to Thomas Luttrell of Luttrellstown, with a stipulation that fit chaplains be provided for the church. Field inspection in the late twentieth century identified two distinct phases of construction in the walls: larger limestone blocks below, bonded with white mortar, and smaller masonry higher up, bonded with cream-coloured mortar.

The church stands close to the western boundary of Aderrig parish, which also marks the county boundary with Kildare, roughly 200 metres east of that boundary. The graveyard enclosure surrounding the ruin is difficult to trace on the ground. By 1857, a local antiquarian noted that the old approach road, Aderrig Lane, had been absorbed into adjoining farmland. The south doorway, with its pointed segmental arch edged by large plain stones and a bolt hole on the west side, is the better preserved of the two entrances, though ivy now covers much of it. Putlog holes, the small openings left in a wall when timber scaffolding poles are removed during construction, are visible in both the north and south walls at about one metre from ground level, offering a small but legible trace of the building's original assembly.