The antiquarian Thomas Westropp, writing in the early twentieth century, believed the water-mill had stood within the castle's bawn, the enclosed yard or courtyard that typically surrounded an Irish tower house and its outbuildings. Survey work later established that the mill race, the channel cut to carry water to drive the mill wheel, actually runs some distance to the west and north of the castle. The ruins visible on the Ordnance Survey map, to the south-east of the castle and sitting directly on that mill race, are now considered the more likely candidate for the medieval mill itself.

The mill race gives a sense of the scale of the original installation: roughly one metre deep and three to four metres wide, it is substantial enough to have served a working agricultural community for generations. The mill is first recorded in an extent of 1298, when it was valued at thirty shillings, placing it firmly within the medieval manorial economy of Limerick. By the mid-seventeenth century, it was still a going concern. The Civil Survey of 1654 to 1656 recorded that Henry, Earl of Bath, held Glenogra at that time, and among his possessions were a castle, a bawn, thirty houses and cabins, a mill, and the legal rights of a Court Leet and Court Baron, the latter two being local administrative and judicial courts associated with manorial landholding.

The site is a quiet one, and visitors should not expect a preserved structure. What remains is largely a matter of earthworks and the visible course of the mill race, best appreciated by consulting the relevant Ordnance Survey sheet before visiting and cross-referencing the mapped position of the ruins with the landscape on the ground. Aerial photographs held by the Archaeological Survey of Ireland, taken in September and October 2002, offer a clearer view of how the features relate to one another across the broader Glenogra complex. The relationship between the castle, the bawn, and the mill race repays careful attention, particularly for anyone interested in how medieval settlement patterns organised themselves around water and economic infrastructure rather than purely defensive considerations.