Sully Family Genealogy Forum
I have this vague memory of a story that a noble named Sully was involved as an accomplice of William of Normandy in the invasion of England in 1066. As a reward for his thuggery he was granted estates in western England. This might account for the profusion of Sullys in Somerset.
This would be a completely different group from those associated with the Duc de Sully, and his chateau on the River Loire, which dates from the 17/18th century. If you get a chance to visit this castle, do so . It is fabulous.