The authors agree that this surname derives from place names very widespread in the Italian peninsula, all linked to the term casale, which designated originally a dwelling or rustic building, or a plot of land with a farmhouse. From that base term also arose variants such as casaletto, casalino and casalone.

E. De Felice notes that the place names Casale, Casaletto and Casalino are widely distributed throughout peninsular Italy, while other variants have a more limited distribution: Casaglia is frequent in Tuscany and in Emilia-Romagna; Casaleggio and Casalegno are peculiar to the north and centre-west of Italy, with Casalegno of Piedmontese rooting; Casareggio and Casaregis are peculiar to Liguria.

E. Rossoni specifies that Casale presents greater concentration in the northwest and in southern Italy, especially on the Tyrrhenian coast, and that Casali is more widespread in the centre-north. Both forms could derive from place names present in areas such as Milan, Parma, Mantua, Caserta and Grosseto, or from nicknames that alluded to the place of origin of their bearers, with the sense of "those of the casale".