What makes Cahermakerrila quietly unusual is not just its age but the way later generations kept grafting themselves onto it. Two rectilinear drystone structures, one identified by the antiquarian Thomas Johnson Westropp in 1915 as an old oblong house and the other as two ruined cabins, are pressed against the cashel's outer wall on its south-east and south-west sides. They do not appear on the 1842 Ordnance Survey six-inch map but are visible on the 1897 twenty-five-inch edition, suggesting someone was still making practical use of a structure already ancient by the time they arrived.

The cashel itself is subcircular, measuring roughly 34 metres north to south and 33 metres east to west, with a drystone wall up to four metres wide. The outer face is carefully constructed, with large limestone blocks, each about a metre long and a metre high, forming the base, and smaller slabs tapering toward the top. The wall survives to an external height of up to 2.6 metres along its north-east arc, where two stone buttresses also project outward, the larger of them rising to around two metres. A displaced lintel stone lies near the entrance on the south-east side, a reminder that the opening was once properly finished. Inside, a collapsed drystone wall meanders across the middle of the enclosure, and the remains of a hut site occupy the north-east interior. The name itself carries a genealogical thread. Westropp traced the eponymous figure, the son of Irial, to a branch of the Corcamodruadh tribal grouping, associated with the O'Conor and O'Loughlin families, and placed him at around 1430 or later. He was careful to note, though, that forts in Ireland are commonly named after later occupants rather than original builders, so the cashel's foundation could be considerably earlier. The Irish form of the name, Cathair Mhic Oirialle, as recorded on Tim Robinson's 1977 map of the Burren, preserves that lineage more legibly than the anglicised version.

The site sits within a large multiperiod field system, with further enclosures and hut sites clustered to the west and south-west, and a house of indeterminate date about nineteen metres to the south-east. From the rise, Slieve Elva is visible to the north-north-west. The whole landscape has the quality common to the Burren: everything built here was built from the same grey limestone that surfaces underfoot, making it easy to walk past a wall that has been standing for six centuries without quite registering what it is.