The fragment, roughly fifteen metres long and running north to south, forms part of the original east wall, built directly into the base of a steep hill. To its west, grass-covered mounds of rubble mark where the rest of the structure once stood, tucked into a narrow strip of land between the hillside and a stream, exactly the kind of confined, water-adjacent site that millers sought out.

The scale of what has been lost becomes clearer when you consider how the mill was described during a survey carried out between 1633 and 1636, which recorded it as a "good English mill here, one of the best in the country", a phrase cited by the Sligo antiquarian W. G. Wood-Martin in his 1889 work on the county. The term "English mill" in this period typically referred to a vertical waterwheel mill, a technology associated with the plantation era and distinguished from the older horizontal-wheeled mills, sometimes called Norse or Celtic mills, that had long been used across Ireland. To be ranked so highly at that particular moment suggests the Rathbraghan mill was a substantial and relatively sophisticated installation, serving what would have been a significant local agricultural economy. The precise circumstances of its demolition are not recorded.