These grounds, known in Irish tradition as cillíní (the singular is cillín), were used for the burial of unbaptised infants, and occasionally others considered to exist outside the formal rites of the Catholic Church, including stillborn babies, foundlings, and sometimes suicides or strangers. Because the Church denied such individuals burial in consecrated ground, communities established their own quiet, liminal spaces for them, often at the margins of townlands, beside old walls, at the edges of bogs, or within the earthworks of earlier monuments.

The cillín at Kilgreana is one of hundreds recorded across Mayo, a county where the tradition persisted well into the twentieth century. The placename Kilgreana likely derives from the Irish, with the element "cill" pointing to an early ecclesiastical enclosure or cell, suggesting the site may occupy ground with a much longer devotional history than its more recent use implies. Cillíní were rarely marked with headstones, and many survive today as low, grassy enclosures, identifiable mainly by their slightly raised ground or a surrounding boundary of stone, easy to walk past without recognition.