The present character of Felin Cochwillan is thought to date from the late-nineteenth century, but there was a mill on the site before 1560. In c1800 it was a fulling mill, which was acquired by the Penrhyn Estate and converted to a corn mill. The present five-bay, two-storey building is aligned roughly north-south, constructed of rough rubblestone with large windows with slate sills; with stone voussoirs forming cambered heads to the ground floor windows and slate lintels to the first floor windows. The pitched slate roof has gabled dormers facing east.

The miller's house occupies the northern bay and a single-storey extension on the east side. The mill occupies the rest of the building, with a large breast-shot wheel on the west side, fed by a slate slab-lined leat from the Afon Ogwen. It drove four pairs of stones, two driven by stone spindles and stone nuts from the great spur gear, and two by flat belts from a wooden pulley mounted on the upright shaft. A crown wheel at the top of the upright shaft drives layshafts with wooden pulleys, which in turn drove flour dressers, an oatmeal shaker and winnower, and the sackhoist. At the south end of the mill is a lean-to drying kiln, with a rectangular fireplace built of slate slabs, and a perforated tile floor above.

Information from Cadw Listed Buildings database 9 March 2000, and Felin Cochwillan website.
W J Crompton, RCAHMW, 23 April 2014.