The manor of Dunster was held by Aelfric in 1066 and by William de Mohun in 1086. This Norman lord was granted nearly 60 estates in Somerset, and became the county's sheriff c.1083. He established Dunster as the seat of his barony and built a castle there. He retained the manor for himself rather than farming it out. By 1131 he had been succeeded by a son, William II de Mohun, who was dead by 1155. This son was created Earl of Somerset by the Empress Matilda in 1141, but the earldom was not passed on to his son, William III although the barony and estates were. William IV (d.1193), his son, inherited, and at his death in 1193 his son Reynold was a minor, so did not come into possession until 1204. The estate remained in the Mohun family throughout the medieval period.
The church (specified as St George's) was given by the first William de Mohun to his foundation of Bath Priory in c.1090. There may have been monks at Dunster shortly afterwards, but the priory was not formally set up until c.1330. The advowson was in the hands of Bath Priory from c.1090 until the Dissolution.