The authors agree that this surname derives from place names formed on the base casa and its variants, such as Casella —in the Genoa or Treviso areas—, Caselle —in the Verona, Treviso, Bologna, Salerno or Lodi areas— and Casellina di Scandicci, in the Florence area, all documented since medieval times.

F. Miranda broadens this etymological base by noting that the surname could also have originated in names of minor localities, particular buildings or small inhabited centres, always derived or compounded on casa and its altered forms. He adds that the surname is present in almost all the regions of Italy, with greater concentration in Lombardy, Sicily, Campania, Emilia-Romagna, Liguria, Calabria, Lazio, Piedmont, Tuscany and Veneto.

E. Rossoni specifies that the variant forms have their own regional distributions: Caselle is characteristic of the Potenza area, especially of Melfi and Barile, while Caselli is typical of Emilia-Romagna and Tuscany.