Llantrisant Castle is a ruined castle in Llantrisant, Rhondda Cynon Taf, Glamorgan, Wales. The ruins are on a good elevation, commanding extensive views of the surrounding country. It has the appearance of once occupying a formidable position of defense. Now only a portion of a tower and some outer walls remain standing and neglected. Its origin being ascribed to different dates. During what period and by whom this and several other castles in Wales were erected, has not been determined.