The mill at Rathganny sits close to the village of Multyfarnham, and the possibility that it stands on or near the site of a medieval mill connects a relatively modest piece of rural infrastructure to centuries of milling activity along the same stretch of water.

The evidence for that older mill comes from a description written in 1682 by Sir Henry Piers of Tristernagh, a local landowner and antiquary whose account of the River Gaine traces the watercourse mill by mill and bridge by bridge. Piers noted that the river passed through Multyfarnham, fell under a large bridge, and ran "thence to a mill, whence immediately it watereth the ground of the late Friery of Multifernan." The friary he referred to was the Franciscan house at Multyfarnham, founded in the medieval period, and the mill he described appears to have served or been associated with it. Mills attached to monastic houses were common in medieval Ireland, providing the community with ground grain while also, in many cases, serving the surrounding tenants. When the first edition of the six-inch Ordnance Survey was published in 1837, a corn mill was recorded in precisely this area of the Gaine's course, suggesting a continuity of use on the same stretch of river, even if the building itself had changed over the intervening centuries.