It measures twenty-three metres across in both directions and stands only thirty centimetres above the surrounding terrain, defined by a shallow fosse, essentially a ditch dug to mark or defend a perimeter, that is barely fifteen centimetres deep and under two metres wide. The fosse appears only intermittently around the circuit, showing most clearly at the northern and southern edges. No original entrance has been identified.

This kind of earthwork is generally understood to be a ringfort or rath, a category of enclosed settlement that was built and used across Ireland primarily during the early medieval period, roughly between the fifth and twelfth centuries. They served as farmsteads and enclosed spaces for livestock as much as defensive structures, and they are found in their thousands across the Irish landscape. What makes the Mullaghboy example quietly interesting is its setting. Drumlins, the elongated hills of glacially deposited material that ripple across much of Ulster and north Connacht, were favoured ground for early settlement builders, offering drainage, elevation, and visibility. Positioning a fort at the crest of a drumlin ridge, even a short one, was a deliberate choice. Adding another layer of interest, a second rath sits approximately one hundred metres to the south, suggesting this was not an isolated dwelling but part of a small cluster of related enclosures, possibly occupied by members of the same kin group or used across successive generations.