The pond near Glassan, Co. Westmeath, visible on the first edition Ordnance Survey six-inch map of 1837, carries within it the faint outline of a milling history that reaches back at least to the mid-seventeenth century, when Irish cartographers were methodically recording the country's landscape for the Cromwellian administration.

The Down Survey, carried out in the 1650s under Sir William Petty, was a vast mapping project intended to facilitate the redistribution of land confiscated from Catholic landowners. Its map of Kilkenny West barony, dated 1659, depicts a watermill with a vertical waterwheel set into the gable of a building on a riverbank, annotated simply as 'mill'. The accompanying terrier, a written description of the surveyed lands, notes that on the lands of Bunowen there stood both a castle and a mill, the latter on property belonging to Pierce Dillon, described as an Irish papist in 1641. On the Down Survey map, the mill appears to sit at the convergence of three townland boundaries, the areas now known as Farrannamoreen, Pearsonbrook, and Glassan. By 1837, the Ordnance Survey was recording a Corn Mill in Glassan and a mill pond in the same general vicinity, the pond lying to the north of the stream near Pearsonbrook. Whether the nineteenth-century corn mill was built directly on the footprint of Dillon's earlier mill, or simply inherited the same watercourse, is not certain. The cartographic evidence suggests continuity of use across two centuries, even if the structures themselves changed.

The site sits in a landscape where the boundary lines of old townlands still follow the natural logic of streams and low ground. The mill pond at Pearsonbrook and the Corn Mill at Glassan bracket a stretch of water that once turned a wheel for a Catholic landowning family in the years just before the upheavals of the 1640s reshaped who owned what across this part of Westmeath.