As described in historical dictionaries

An Etymological Dictionary of Family and Christian Names (1857)

(origin: Cor. Br. Local) The crow's hill; from Bren, a crow, and dun or don, a hill.

Arthur, William (1857) An Etymological Dictionary of Family and Christian Names. New York: Sheldon, Blakeman. Public Domain.


Patronymica Britannica (1860)

BRENDON. An estate in St. Dominick, CO. Cornwall, possessed by the family in earlj' times.

Lower, Mark A (1860) Patronymica Britannica: a dictionary of the family names of the United Kingdom. London: J.R. Smith. Public Domain.


BritishSurnames.uk is a Good Stuff website.