Tyn y Graig is situated on the ledge of a rocky shelf on Mynydd Rhiw below the church of St Aelrhiw. The walls of uncoursed boulders are of one build with original openings, and there are two tall square capped chimneys with drip ledges. The slate roof is a replacement of former thatching. Cut into the face of the east wall is an inscription ww1/1762. The SE room is separated from the entrance passage by a wooden partition , mostly modern, but retaining the original in and out work at the east end The dairy with loft over it at the outer gable end is an unusual but original feature. The stair has stone treads built in with the projecting wing. The attic storey has no features of note.

Details of the plan and quality of the woodwork suggest a date at the beginning of the 18^th century rather than earlier, but it is unlikely to be as late as the inscription would suggest. William Williams, who lived in Plas yn Rhiw in 1776, owned the property at that time.