The name 'Old Cwm Mill' is found only on the modern map, but refers to buildings which are shown, but not named, on all three editions of the 25-inch O. S. maps, dating from 1882, 1901 and 1921. The location is only 60 metres north-west of Lower Cwm Mill (NPRN 40071), which may have superseded the Old mill. Water came from the Cas-Troggy Brook which drove a number of mills in the valley, via a 300 metre-long mill race which could have supplied both mills.
W J Crompton, RCAHMW, 5 May 2011.