E. Rossoni notes that this surname presents specific areas in Piedmont, especially in the Cuneo, Turin and Asti areas, as well as in the Treviso area, in the Ferrara area and in Rome. According to Rossoni, the surname and its variants would derive from the numerous place names that contain the root Casetta or similar, present in central-northern Italy. The variant Casette is very scarce and is located in the Venice area. Casetti presents areas in the Cremona area, in the Trento area, in the region of Emilia-Romagna and in the Rome area. Casetto, for its part, has specific presence in Piedmont, Lombardy and Veneto.

F. De Laurentiis proposes a different etymology: he considers that the surname is an affectionate or diminutive derivative of casa.