The site is a ring-barrow, a type of low, circular earthen mound typically surrounded by a ditch and outer bank, used for burial during the Bronze Age and occasionally into the early medieval period. This one remained unrecorded on any official cartographic survey until aerial photography brought it into view.

The monument was first identified during a systematic aerial photographic survey of the Bruff district in 1986, when it appeared as a circular cropmark on the survey image catalogued as Bruff 58(03). Cropmarks form when buried features such as ditches or banks influence the growth of grass or grain above them, producing patterns visible from altitude that are otherwise undetectable at ground level. Decades later, a Google Earth orthoimage taken on 18 November 2018 confirmed the site again, this time as a U-shaped cropmark, suggesting the circular outline is partially obscured or incomplete in that particular image. The barrow lies in pasture just north of a linear drainage ditch and east of a field boundary, and it is not alone in the landscape: several other ring-barrows are recorded immediately to the west and north, hinting that this corner of Limerick once formed part of a more extensive funerary complex. The record was compiled by Martin Fitzpatrick and uploaded in July 2020.

Because the feature survives only as a cropmark rather than as an upstanding earthwork, there is nothing obvious to see from the ground. The field at Knocknacrohy looks, to most eyes, like ordinary grazing land. The best conditions for cropmark visibility from aerial or satellite imagery tend to occur during dry summers, when soil moisture differences above buried features become more pronounced. Anyone with a particular interest in the site can examine the Google Earth imagery directly, or consult the National Monuments Service record, where the 1986 aerial survey image provides the clearest picture of the barrow's circular form and its relationship to the neighbouring monuments.