The authors agree that this surname is proper to the Milan area and its zone of influence, and that it derives from terms related to trade: the Latin mercator ("merchant"), which evolved towards medieval forms such as mercadore or mercante. By the 16th century the term had developed into the form mersator, the antecedent of the later dialect variants; the surname is frequent in the Brianza region and nearby areas.

E. Rossoni specifies that the fixing as a surname can be traced to around 1600 in Milan, and mentions as a notable figure the count palatine and senator Desiderio Merzagora, who died on 3 March 1646. Surnames in Italy, for its part, places members of these families in documents as early as the 14th century in Milan, and refers to a Desiderio Merzagori as captain of the burg of Monza in the 16th century.