The conversion, carried out around 2000, preserved a great deal of the original fabric, and the restored overshot waterwheel, a type in which water is delivered from above to push the wheel around, remains visible on the western side of the building, still set into its original cast-iron watercourse. Nearby, the ruins of the corn kiln survive to the north, where grain would once have been dried before grinding, and the silted-up millpond sits to the southeast, the old millrace having run from it, over the wheel, through a culvert beneath the road, and away to the northwest.

The present limestone structure dates to around 1810, built on an L-shaped plan over two storeys, with the southern section added as a later extension. It was altered again around 1900, and its coursed rubble limestone walls and square-headed window openings give it the plain, functional look common to Irish agricultural industry of that era. Intriguingly, there may be considerably older roots beneath this early nineteenth-century fabric. A watermill is marked on the 1657 Down Survey map of Fore barony, a mid-seventeenth-century land survey commissioned under the Cromwellian administration, and that mill is shown standing precisely at the boundary between the townlands of Foyran and Rathshane, in the same area where Balnacart Mill appears on later Ordnance Survey maps. Whether the later mill was built directly on the foundations of its predecessor or simply occupied the same favourable stretch of water is not certain, but the continuity of use across several centuries is striking in itself.