The authors agree that this surname derives from the Lombard term wizza, which designated a wood or a plot of common property, and that the bearing family would be associated with that type of social organization of the land. Surnames in Italy places the origin in the Sebino area, the lake district of the province of Bergamo.

E. Rossoni notes that a derivation from the medieval name Guittius or Guizzo is also possible, documented in a deed of 1259 in Siena, which would open a second line of origin independent of the toponymic or social explanation. Rossoni further records the presence of this surname in Solto Collina, in the Bergamo area, during the 18th century.

As for its distribution, Rossoni indicates that Guizzetti is proper to the Bergamo and Brescia areas, in Lombardy. The related forms show different distributions: Guizzi is concentrated in the Brescia area, while Guizzo is typical of the Treviso area and of Friuli-Venezia Giulia, in north-eastern Italy.