The trees, which have colonised both the interior and the bank itself, give the enclosure an oddly secretive quality, obscuring a structure that was originally designed to project authority across open ground.

Ringforts, known in Irish as raths, are single or multiple enclosures typically dating from the early medieval period, roughly the fifth to the twelfth centuries, and were used as enclosed farmsteads by the farming families of Gaelic Ireland. The Coolnagillagh example is circular and slightly raised, measuring 31 metres north to south and 28.5 metres east to west. It is defined by an earthen bank rising to 1.25 metres, with an external fosse, a defensive ditch, reaching a depth of 1.45 metres along its eastern and north-eastern arc, and a low counterscarp bank running from the east around to the south-south-west. The entrance, 6 metres wide, faces east and is approached by a causeway crossing the fosse. Additional gaps in the bank to the north-east and west are likely later disturbances rather than original features. A note published by Broker in 1937 records a double fence enclosing the interior, a detail that suggests the site retained some visible internal structure well into the twentieth century, though no further description of it survives in the available record.

The site sits on an east-facing slope with a notably clear prospect north-east along the Owenbaun valley, a position that would have made practical sense for anyone keeping watch over livestock or monitoring movement through the landscape. The dense planting of conifers across the bank and interior now partially blocks that view, and also makes the earthworks themselves harder to read from within, though the outer profile of the bank and the fosse remain legible from the surrounding pasture.