The carving is worn nearly smooth now, but the ornamental ambition is still legible, and the current position of the doorway, set into the nave's north wall rather than the more conventional west gable, is likely the result of a deliberate relocation sometime in the 1400s. That kind of structural tinkering, moving a fine earlier feature to serve a later arrangement, is not unheard of in Irish medieval churches, but it gives this particular ruin an additional layer of strangeness: the building has been quietly reorganising itself across the centuries.

The site appears in the Medieval Papal Chancery documents of 1260 and in the Papal Taxation records of around 1306, both times under the name 'Kilsilan'. That name may preserve the memory of Sillan, identified as either the Abbot of Bangor or a saint recorded in the Irish martyrologies. Whatever its dedication, the church is a multi-period structure: the earliest fabric is the chancel, which predates the Romanesque period entirely, and which became a chancel only when a nave was added in the twelfth century. The chancel is now very ruinous, with only the round-headed chancel arch and a short length of the south wall still standing. The west gable tells a different story again: a bellcote, an ogee-headed window, and a garderobe chute, a small projection used to discharge waste, all point to construction or significant rebuilding in the fifteenth century or later. By the time of the Civil Survey of 1654 to 1656, the building was already described as 'a little Church unroofed'.

The fabric itself rewards close attention. The walls are built from large blocks of sandstone and limestone, roughly coursed, with small flat stones pinned into the gaps. At the north-east and south-east angles of the nave there are the remains of engaged columns, bases and a capital still in place, details that suggest the interior once had more architectural pretension than its current state implies. The sole surviving original window is in the south wall, and only the east side of its embrasure remains. Inside the nave, a seventeenth-century slab lies on the ground. The church sits about 170 metres east of Kilsheelan village, just south of the main road and immediately north of the Suir.