What makes the site at Derrynagarragh quietly compelling is not just its age but the way successive maps, separated by nearly two centuries, appear to place a working mill in the same spot on the same streambank, suggesting a continuity of use that outlasted wars, land transfers, and the upheavals of the early modern period.

The documentary record opens in 1647, during the Wars of the Three Kingdoms, when a levy of £15 was imposed on a group of mills across Co. Westmeath to fund Captain Ignatius Nugent of the Irish Confederate Army, the loose Catholic and royalist coalition then contesting control of Ireland. Of that total, £1 8s was charged specifically against Edward Fay for his mill at Direnegaragh, the spelling used in the Calendar of State Papers Ireland. The mill at that point was already described as medieval in origin, meaning it almost certainly predates the Confederate period by several generations. A decade later, the Down Survey of 1657, a large-scale mapping project commissioned by the Cromwellian administration to catalogue confiscated Irish land, recorded a mill in Teagheltowne parish, known also as Faughalstown, and depicted it in a notably specific way: a vertical waterwheel mounted on the gable end of a building beside a stream. A vertical wheel of this kind, turned directly by the flow or fall of water, was the more technologically complex of the two main mill-wheel types, requiring a head of water sufficient to drive the wheel with enough force to turn the millstones above. When the first edition Ordnance Survey six-inch map was published in 1837, it marked a corn mill in a location that corresponds closely to the Down Survey site, raising the likelihood that the same spot was in continuous or near-continuous use for grinding grain across at least two centuries of documented history, and probably longer.