These sites, whose name derives from the Irish "cillín" (a small church or cell), were used for centuries to bury unbaptised infants and others considered, under Catholic doctrine, ineligible for consecrated ground. The choice of a pre-Christian monument as the location is characteristic: such liminal places, neither fully of the church nor entirely outside it, became quietly understood as appropriate for those who existed in a similar threshold state.

The site occupies a subrectangular area measuring roughly 20.5 metres east to west and 16.5 metres north to south. Its eastern boundary is formed by the bank of the ringfort itself, a type of enclosed farmstead common in early medieval Ireland, typically defined by one or more earthen or stone ramparts. Possible traces of a separate enclosing wall are still visible at the south-east and north-north-west, suggesting the burial ground was at some point deliberately demarcated within the larger structure. Small set stones in the interior mark graves oriented east to west, a Christian burial convention pointing the dead toward the rising sun. The site was noted by O'Flanagan in 1927, and the orientation of those modest grave markers indicates use well into the post-medieval period, even if the precise span of activity remains unclear.

The graves themselves are marked only by those small stones, nothing inscribed, nothing raised, which reflects both the informal nature of cillín burial and the grief that surrounded it. Families who buried children here did so quietly, often at night, without a priest. The ringfort that contains the killeen is a separately recorded monument, and the layering of one kind of boundary, the Iron Age or early medieval rath, beneath another, the sorrowful geography of unofficial burial, gives the place an unusual density of human meaning.