Priordy Trefynwy oddeutu 1080, fel Priordy Urdd Sant Benedict gan y Llydäwr, Gwethenoc, a parhaodd nes diddymu'r mynachlogydd yn 1536. O 1814 hyd 1973 bu'r adeilad presennol yn un o ysgolion cynradd y dref.

English translation: "Monmouth Priory Was founded c1080 as a Benedictine Priory by Gwethenoc, a Breton from Saumur. The Priory continued until the Dissolution of the Monasteries in 1536. From 1814 until 1973 this surviving building was used as one of the town's primary schools."