The circle in question sat on the southern lower slope of Knocksentry Hill, also known as Knockroe, roughly 650 metres east of the lake's northeastern shore. By the mid-twentieth century, as O'Kelly noted in 1944, there was nothing left to see and nobody nearby who could recall it ever standing.

The circle's existence depends almost entirely on a single early source. T. Crofton Croker's map of 1833 recorded a third stone circle on Knockroe, positioned to the east of two others that still survive today, known as Circle O and Circle P, which stand 40 and 100 metres respectively from the lost site's approximate location. Writing in 1833, Corker described the circle as measuring 28 yards, or roughly 25.5 metres, in diameter, with a circumference of around 103 metres. By 1900, Edward Barry was already reporting that the Ordnance Survey had not marked any of the three Knockroe circles on its maps, and that only two remained on the ground. The third, he noted, was shown on Croker's earlier survey lying further east. That it was a genuine monument seems reasonable given the density of prehistoric activity in the immediate area: a cist burial cemetery, a type of prehistoric grave formed by stone slabs, lies 140 metres to the northwest, and several mound sites cluster nearby. What brought about the circle's disappearance is not recorded.

The site sits in pasture on private farmland and is not formally marked or accessible as a visitor destination. Its approximate location has been tentatively identified from Google Earth imagery taken in June 2018 and September 2020, though it is not visible in earlier aerial photographs from 2005 or the early 2010s. Anyone with a serious interest in the archaeology of Lough Gur is better served by the surviving monuments in the area, including the great Grange stone circle to the north, which is one of the largest in Ireland. The lost circle on Knockroe is most usefully understood as a reminder that even well-studied landscapes hold sites that slipped through the documentary record before anyone thought to look carefully enough.