Pentre FFynnon Mill was a Mostyn Estate mill attached to Pentre Ffynnon Farm. The building has two storeys and an attic, and is constructed of sandstone rubble under a shallow hipped, slated roof. A door frame on the east-facing front bears the initials IW and the date 1823. A later, single storey lean-to three-bay cartshed has been built against this east side, its corrugated iron roof supported on stone piers. The west elevation has a blocked cart opening, and three iron-framed windows in chamfered stone surrounds. The waterwheel was underground, and the pit is covered by a steel grille; part of the composite high-breast-shot wheel remains in situ. Inside the mill the wallower and wooden upright shaft survive, with two bedstones on the first floor, and an iron extension to the upright shaft carrying a crown wheel which drove horizontal shafts with wooden pulleys.

Information from Cadw Listed Buildings database, 25 May 2001.
W J Crompton, RCAHMW, 23 April 2014.