Plasau Duon or Plasauduon is a timber-framed house, formerly in the parish of Carno, but now within the area of the community council of Caersws in the historic county of Montgomeryshire, and now in Powys, Wales. It is located on a site above the left bank of the Afon Carno, on a farm road leading off the lane from the A.470 to Bwlch-y-garreg. It is a fine example of a ‘’Severn Valley’’ house and has a Grade II* listing. It is likely to have been built in the second half of the 16th.