The site at Killian is roughly subcircular in plan, measuring about 83 metres north to south and 74 metres east to west, and its boundary is formed by a spread of stone that has largely sunk and spread into the surrounding ground. The northern section survives best, rising to just over a metre on its interior face, but elsewhere the wall has slumped to little more than a low, mossy ridge. It is the kind of boundary that registers as a landscape feature before it registers as a monument.

Within that boundary, two finds of a different order complicate the picture considerably. A children's burial ground occupies the interior, a reminder of a practice once widespread across Ireland whereby unbaptised infants were interred in liminal, consecrated-adjacent spaces, neither fully within nor fully outside the sacramental order. Such sites, often called cillíní, frequently cluster around early ecclesiastical enclosures, and Killian follows that pattern. Equally suggestive is a bullaun stone placed inside the perimeter at the south-west. A bullaun is a rounded depression, or series of depressions, ground or naturally formed into a boulder; they are associated with early Christian sites across Ireland and are thought to have served ritual or practical functions, though their precise uses remain debated. The combination of enclosure, children's burial ground, and bullaun points toward a site of some early ecclesiastical significance, even if nothing above ground announces it as such. The entrance, now modernised and about three metres wide, sits at the south-west, close to where the bullaun stone stands.