The Johnston family's double mortuary enclosure, a two-chambered walled structure nearly fourteen metres long and standing up to 2.8 metres high, almost certainly incorporates masonry from the original parish church, though no section of that earlier building can now be clearly identified. An inscribed stone on the outside of the west wall carries a date that reads 176-something, the final digit lost, and the oldest graveslab inside commemorates one Baptist Johnston, dated 1710. It is an odd palimpsest: a burial structure built partly from the bones of a place of worship, itself long since abandoned.

The church at Donagh appears in the ecclesiastical taxation of Pope Nicholas IV, recorded between 1302 and 1306 under the name Dunagh, and the names of individual clergy serving here are known from as early as 1451. By 1622 the building was already described as ruinous, and before the century was out, the parochial centre for Protestant worship had shifted to Glaslough, roughly two kilometres to the north-east. The site has occasionally been confused with a similarly named church in County Fermanagh, Domhnach maighe dá Chlaoine, meaning the church between the bogs, a mix-up that points to how easily early ecclesiastical place-names can blur across county boundaries. What the medieval building looked like can only be guessed at from fragments: a doorway arch and a stone corbel carved with the head of a cleric in relief were removed to Monaghan County Museum in the 1970s, and a decade later a window jamb fragment decorated with a keel moulding, a rounded, ridge-like decorative profile common in Romanesque and early Gothic stonework, was also acquired by the museum and dated to the late twelfth or early thirteenth century. Part of a ringed cross head, recorded at the site in the 1930s, followed the same route.

The graveyard itself, a roughly triangular enclosure defined by earthen banks and hedges, contains a cup-marked stone, the Donagh cross, two cross-bases, two seventeenth-century graveslabs, and a cross-shaped headstone dated 1666. The headstones more broadly run from the late eighteenth century into the mid-nineteenth. There is space for about three cars outside. The more architecturally significant pieces from the site are now in Monaghan County Museum, which is worth bearing in mind before visiting with the expectation of carved stonework in situ.