The authors agree that the base of this surname is the medieval name Ciardo, a reduced form (aphaeretic hypocoristic) of Ricciardo, an archaic variant of Ricardo. E. De Felice notes that this medieval name is documented in Florence in 1260 (Ciardus), and adds that in some cases it could also derive from the medieval names Acciardo, Bocciardo or Guicciardo. E. Rossoni provides additional documentary testimonies: the notary Ser Pietro di Ciardo in Siena in the 14th century, and Giuliano Ciardi in Florence in the 15th century.

On the geographical distribution, De Felice indicates that the surname is spread in the southern peninsula, while the forms Ciardi, Ciardetti and Ciardini are concentrated in Tuscany. Rossoni specifies in greater detail: Ciardi presents areas in the Florence area, in Lazio, in Campania and in Puglia; Ciardini is peculiar to the Florence area; Ciardino is Campanian; Ciardiello is located in Naples and in localities of the Avellino and Caserta areas; Ciardulli appears in Rome, Naples and in the Caserta and Avellino areas; Ciardullo has presence in Rome but with its main nucleus in the Cosenza area. Rossoni also notes that Ciardo is characteristic of the Salento area —that is, the southernmost zone of the region of Puglia, in southern Italy— and could likewise derive from a place name.