These were the resting places of unbaptised children, and in some cases of others considered ineligible for consecrated ground, including stillborns, suicides, and strangers whose origins were unknown. The one at Cooleen in County Mayo is one such site, quietly occupying its place in the landscape without monument or signage to explain what it is.

The practice of burying unbaptised infants in separate, unconsecrated ground was rooted in the theological position, long held by the Catholic Church, that those who died without baptism could not enter heaven and therefore could not be buried in a churchyard. Rather than leave their children without any formal resting place, families brought them instead to liminal spaces, locations that existed at the edges of the ordinary world, old ringfort boundaries, the margins of bogs, the shores of lakes, or the ruins of early medieval churches. Some cillíní were used continuously for centuries, accumulating generations of small unmarked graves. The land at Cooleen represents this tradition in Mayo, a county where such sites are relatively numerous, reflecting both the density of rural settlement and the persistence of the custom well into the twentieth century.

Because the site carries no formal interpretation and the available record is limited, little more can be said with certainty about its precise boundaries or condition. Many cillíní have no visible grave markers at all, or only simple stones laid flat without inscription. Visitors who come across such places are generally advised to treat them with the same quiet respect they would offer any burial ground, which, in every sense that matters, they are.