What makes the site quietly peculiar is not its ruin, but its near-total silence as a burial ground. The subcircular earthen enclosure surrounding the church, roughly 34 metres across and defined by a low bank on its eastern, southern, and north-western sides, contains almost no evidence of interment. A single headstone dated 1806, found inside the nave itself rather than in any surrounding churchyard, is all that remains of the dead.

The church was dedicated to St Deignian, identified by scholars as the Welsh saint known as Decumen, who died around 706 AD and whose cult carried across the Irish Sea during the early medieval period of intensive contact between Wales and the south-east of Ireland. A chapel at Little Killiane under this dedication was recorded by a writer named Synnott around 1680. Earlier still, a formal ecclesiastical visitation in 1615 by Thomas Ram, the Protestant bishop of Ferns, noted that one Phillip Rawe was serving as curate of Killalan, and that both the church and its chancel were then in reasonable repair. That the building declined so completely in the centuries following is something the structure itself quietly documents. The nave walls survive almost to their full height, with well-cut corner stones and two pointed doorways of uncut stone, each fitted with hanging eyes for the original door furniture. The chancel, by contrast, has been reduced almost entirely to foundation courses, save for one surviving corner standing to about two metres. The pointed chancel arch between the two spaces, however, remains intact. Lying within the nave is a bullaun stone, a roughly worked boulder with a shallow, deliberately hollowed basin, of a type associated across Ireland with early ecclesiastical sites and sometimes with ritual or curative use.