A cairn, in the Irish archaeological sense, is typically a mound of stones raised over a burial or used as a territorial marker, often dating to the Bronze Age or earlier. This one carries its name on the official record without, for now, much else attached to it.

The notes available for this site are sparse to the point of near-silence. What is known is that the monument has been identified and logged, placing it within a county that contains an extraordinary density of prehistoric remains, from the megalithic landscape of Céide Fields to the passage tombs of the Bricklieve Mountains just across the county border. Mayo's cairns range from modest field clearances repurposed over centuries to deliberately constructed funerary monuments of considerable age. Without further detail on this particular example, it is difficult to say where on that spectrum the Castletown cairn falls, or what condition it survives in today.