The authors agree that the surname derives from the place name Inzago, a locality in the Milan area. E. Rossoni specifies that the surname is proper to the area between Milan and Pavia.

On the origin of the place name, Surnames in Italy notes that in the Middle Ages the locality was called Anticiàcum, a place name of Gaulish origin containing the Roman name Anticius. The hypothesis proposes the existence of a rus anticiacum, that is, a rural property belonging to a certain Anticius. In time, with that reference lost and through dialect simplification, the name became Inzago. It is further noted that in France there are two parallel place names of analogous formation: Anzat-le-Luguet and Anzy-le-Duc.