The authors agree that this surname derives from the place name Guastalla, a town in the province of Reggio Emilia, whose name goes back to the Lombard term wardistall, meaning "guard post" or "place of custody", formed from Germanic roots associated with watchfulness and settlement. Both authors note that the place name is linked to the first phase of that people's settlement in Italy.

V. Blunda stresses that Guastalla was the seat of an autonomous duchy between the 16th and 18th centuries under the Gonzaga dynasty, and that as a surname it survives especially in northern Italy, following the medieval practice of adopting as a surname the name of the lineage's place of origin.

E. Rossoni specifies the surname's geographical distribution: he records a presence in Suzzara and Mantua, in the Gonzaga area and in the Guastalla area. For the variant Guastalli, he notes a small presence in Lombardy and another in the Massa area, particularly in Villafranca in Lunigiana and Bagnone. Rossoni further mentions that the Guastalla formed a noble lineage related to the Gonzaga.