The authors agree that the surname derives from the place name Marengo, found in the Alessandria area and in other localities of Piedmont, and that it is related to medieval forms such as Marencus or marénco.

E. De Felice notes that the surname was formed from the place names Maréngo —in the Alessandria area— and Maréngo-Talloria —in the Cuneo area—, and that it may in part reflect medieval names and nicknames derived from the medieval Latin marincus, with the sense of "of the sea" or "coming from maritime areas".

E. Rossoni broadens the origin with three hypotheses: derivation from the medieval name Marencus, documented from the year 1100; provenance from place names Marengo found also in the Mantua area; and an etymological proposal linking the term with the Marici, an ancient people settled in the territories of the present-day Cuneo and Turin areas, so that Marengo would indicate "descendant of the Marici". Rossoni also distinguishes the distribution of the variants: Marenco spread throughout central and southern Piedmont and Liguria; Marenghi is proper to the area between Parma and Piacenza; and Marengo predominates in the Turin and Cuneo areas.