Abercastle mill is named as Felin Garn on the 1st and 2nd editions of the historic 25-inch O. S. maps. It is an early nineteenth century, single storey and attic structure aligned north-north-east to south-south-west, and is built of rubblestone with a pitched rood of imitation slate. Entry is by a double door at the north end, and a single door from the roadside into the attic storey, with a gablet over where it breaks the roofline. In 1952 the mill had an overshot wheel and two pairs of stones, located at the south end of the building (information from Miss E M Gardener). These have been removed. On the west-north-west side, and at a lower level, is the two storey mill house, with a single storey building linking it to the mill. The house and link are rendered and have slate roofs. At the west end a modern lean-to garage has been added.

W J Crompton, RCAHMW, 3 July 2014.