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Origin and etymology In historic texts In the 1881 census Distribution map

As described in historical dictionaries

An Etymological Dictionary of Family and Christian Names (1857)

(origin: Local) From Trieu, a river in Bretagne, France. Tre signifies a town.

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

BritishSurnames.uk is a Good Stuff website.