The authors agree that the surname derives from the Sicilian dialectal word cardìddu / cardillu, meaning "goldfinch". F. Miranda also notes an alternative etymology: the derivation from hypocoristics formed by aphaeresis of names such as Riccardo or Accardo, and attributes this second reading to the linguist Rohlfs. Miranda documents the first appearances of the surname in historical sources: in Sicily in 1125, where a Stephanus qui cognominabatur Cardillu is mentioned, and in a document of 1363 in Naples, with the reference coram Cardillo Brancacio del Napoli.

V. Blunda rules out the etymology that associates the surname with the Italian cardillo as a simple diminutive, describing it as false, and maintains that the origin is exclusively zoonymic: a nickname applied to people of melodious voice or cheerful character, a frequent motivation in Sicilian surnames based on songbirds, as also happens with Calandra and Carandola.

As for its geographical distribution, Miranda indicates that the surname is present in a large part of the regions of central and southern Italy —especially in Sicily, Lazio and Campania—, with presence also in Lombardy, Puglia, Basilicata, Piedmont and Calabria. Within Sicily, it is concentrated particularly in the Catania, Messina, Palermo and Trapani areas.