The graveyard itself is D-shaped, running roughly eighty metres north to south and fifty metres east to west, its masonry walls following the line of a natural spur of land. The clustered headstones, most of them dating from around 1800 onwards, are concentrated to the south of the present building, and it is there, scholars believe, that the original medieval structure once stood. Nothing of it survives above ground.

The site's history reaches back, at least in tradition, to the early Christian period. The Tripartite Life of St Patrick, a medieval text of uncertain reliability, claims that Patrick established a bishop named Cillín at a place called Tech Taláin, which is identified with this site. By the early fourteenth century, the church was substantial enough to appear in the ecclesiastical taxation ordered by Pope Nicholas IV between 1302 and 1304, listed under the name Thechtalbi. Individual priests serving the parish are recorded from 1432. By 1622, however, when Bishop Spottiswood carried out a visitation of the diocese, he found the building in ruins. In 1638 a local landowner, James de la Field of Derryneshallog, left funds in his will for a small chapel, specified at twenty feet by sixteen feet, to be added to the church; it was probably never built. The congregation eventually got a new building in 1788, constructed at the northern end of the graveyard, and a tower was added to it in 1827. That structure, known as St Cilian's, or occasionally St Sillian's, remains in use today.

What makes the site quietly odd is the layering of absence and continuity. A community has buried its dead on this spur of land for centuries, worshipped in buildings that were successively abandoned, left to ruin, and replaced, and yet the oldest physical layer has been entirely absorbed into the ground. The D-shaped enclosure, a form often associated with early ecclesiastical sites in Ireland, frames a space where the documentary record goes back seven hundred years and the physical evidence stops at the eighteenth century.