This ringfort, or rath as it's known locally, measures approximately 18 metres across its interior and is defined by an earthen bank that rises just over a third of a metre high. Around this protective barrier runs an outer fosse; a defensive ditch about 3.5 metres wide and 0.4 metres deep; with a single causeway on the northeast side providing the original entrance to the enclosure.

The fort's position reveals the careful consideration of its builders. Set on a low north to south ridge about 450 metres east of Mulroy Bay's shoreline, it commands views across the low-lying, marshy grassland that characterises this part of north Donegal. The interior of the fort slopes gently from west to east, following the natural contours of the land. This subtle incline would have aided drainage within the enclosure, an important consideration given the wet nature of the surrounding terrain.

Ringforts like this one at Croaghan were the predominant settlement type in early medieval Ireland, typically dating from around 500 to 1200 AD. They served as defended farmsteads for prosperous farmers and their families, with the circular bank and ditch providing both practical defence and a statement of status within the community. The 4-metre-wide causeway across the fosse would have originally supported a wooden gate or similar structure, controlling access to the homestead that once stood within the earthen circle.