E. De Felice notes that the surname derives from the place name Squillace —whose local form and pronunciation is skiḍḍaci— and from the local demonym squillacioto. Its epicentre is found in Calabria, with a high frequency also in Campania and especially in Sicily, where certain forms in -i are equally typical of the Reggio Calabria area.

E. Rossoni specifies that Squillace is a locality in the Catanzaro area, and that its name comes from the ancient Greek name Skullakion. He distinguishes two variants: Squillace, with a documented presence in the Catanzaro area —including Chiaravalle Centrale— and in localities of the Crotone area such as San Mauro Marchesato, Belvedere di Spinello and Rocca di Neto, besides Stignano in the Reggio Calabria area; and Squillaci, concentrated in the Reggio Calabria area —especially in Motta San Giovanni and Condofuri— and in a Sicilian group of the Catania area that includes Catania, San Pietro Clarenza, Mascalucia and Camporotondo Etneo, besides Messina.

F. Miranda broadens the picture by noting that the surname, together with its variants Schillace and Schillaci, also refers to the same place name, whose ancient name he cites as Skyllation. He proposes two possible etymologies for that place name: the Latin squilla, with the sense of "crustacean" or "small sea shrimp", and the Greek skylakoi, meaning "puppies". Miranda indicates that the surname is diffused in numerous municipalities of Italy, with a large nucleus in Calabria and smaller groups in other regions such as Lombardy, Campania, Piedmont, Lazio, Tuscany and Liguria. In Sicily, he documents a presence in the Catania area —including Acireale and Sant'Agata di Militello—, in the Enna area —with Agira, Troina and Regalbuto—, and also in the Palermo and Ragusa areas.