The church at Lisnasallagh sits on a gentle rise within an active burial ground, its rectangular footprint measuring roughly twenty-three metres east to west and nine metres north to south. What survives is fragmentary: the north wall is the most legible section, standing to about 3.6 metres at its western end before dropping away through a gap and dissolving into low, overgrown rubble toward the east. The south wall has vanished entirely. The west gable leans inward and its north-west corner has already fallen. A low internal crossing wall, about four and a half metres long, survives roughly eight metres from the east end, most likely the remnant of a chancel, the smaller liturgical compartment that in medieval Irish churches typically separated the main nave from the altar area reserved for clergy.

The church is identified with Kilcrumper, known in early Irish sources as Cill Cruimtir, a place described in the medieval territorial document Crichad an Chaoilli as the chief church of the Tuath O Quain, a local dynastic territory in north Cork. The scholar Power, writing in 1932, traced the dedication and argued that the site was founded by St Abban, one of the more widely travelled saints of early medieval Irish tradition, though local memory attached the church instead to St Cruimthir Fraech, a figure whose name is embedded in the placename itself. The church appears in the Papal Taxation of 1291, a Europe-wide ecclesiastical survey that documented church revenues for Rome, which places it firmly within the organised parish structure of late medieval Ireland. By 1615 it was already in ruins, meaning it had been abandoned for decades before that date was committed to writing.

The building is constructed from coursed limestone rubble, the most readily available material in much of north Cork, though the cut-limestone arch fragment lying loose in the graveyard hints that at least some elements were worked to a finer standard. Visitors will find the remains within the graveyard itself, where the church occupies the slight elevation that so often marks early ecclesiastical enclosures in Ireland.