E. De Felice considers that this surname derives from the place name Trezzo sull'Adda, a locality in the province of Milan, in Lombardy.

R. Brondolo proposes a different etymology: the surname would come from the northern Italian dialectal term tres or trésu, meaning "board, transversal piece" and, by extension, "enclosure for livestock" and "dam, sluice". From this word several place names would have arisen, among them Trezzo and Ponte Tresa, and from those place names the corresponding surnames would later derive. Under this interpretation, the relation with the place mentioned by De Felice would not be ruled out, but would be enriched by an older lexical base.