Visit Cornwall asserts that according to local historians the village and parish are named after a Welsh missionary priest named Merryn who came to St Merryn around 650 AD. It has also been proposed that Cornwall's St Merryn was a monk named Maruanus or Maruan. Which Merryn (or alternative spelling) this may be is debatable. Regarding Merryn son of Brychan, in his 1965 book series "The Saints of Cornwall" the scholar Gilbert Doble disputes assertions made by Charles G. Henderson that the Merryn in question may have been the "Marwenna found in William of Worcester's list of the Children of Brychan"