The classification is blunt and honest about its own limits: indeterminate date. That phrase, dry as it sounds, places this structure in a particular category of the Irish archaeological record, one where the physical evidence survives but the chronology does not. It could be a post-medieval farmhouse, a much older dwelling, or something in between. The uncertainty is itself part of what makes it worth noting.

Coollisduff is a small rural townland in Mayo, a county whose landscape holds an unusually dense concentration of abandoned and semi-visible habitation sites, many of them legacy of the clearances and famines of the nineteenth century, though others are considerably older. Without further detail about this particular structure, its walls, plan, or surviving fabric, it sits in a register of places that have been identified and flagged but not yet fully interpreted. The designation as a house monument suggests some visible structural remains, whether standing walls, a collapsed outline, or earthwork traces, but the date range remains open.