What survives is the lower courses of the walls, roughly sixty centimetres high and sixty centimetres wide, built from rectangular-cut stone blocks that emerge here and there through a thick covering of sod. The outline measures about fifteen and a half metres on its longer axis and seven metres across, and breaks in three of the four walls suggest original doorways or openings. Locally, the building is remembered as a church.

The island it sits on, An Toileán Rua, forms the southern tip of Derreens Island. The structure appeared on the Ordnance Survey six-inch map of 1838, one of the earliest systematic mappings of the Irish landscape, which means it was still recognisable as a building at that point. By the time the revised edition was produced in 1921, it had been omitted entirely, suggesting that within those intervening decades the ruin had become too degraded, or perhaps too overgrown, to record with confidence. The gap between those two maps spans a period of enormous disruption in rural Mayo, including the Famine years of the 1840s and the subsequent depopulation of many lakeside and island communities. Whether the building fell out of use before or during that period is not recorded, and no documentary history of the church appears to have survived beyond what local memory has preserved.

The site is on an island, so reaching it requires crossing the lake, and the dense fern growth that covers the ruin means the walls are most likely to be visible in late autumn or winter, when the vegetation has died back enough to reveal the stonework beneath.