The authors agree that this surname derives from the Latin cognomen Iulianus or Julianus. E. Rossoni recalls as a historical point of reference Flavius Claudius Iulianus —known as "the Apostate"—, born in Byzantium in 331 AD and acclaimed emperor in 361. The name was in current use in the Middle Ages, as attested by the Tuscan Iulianus de Pistorio and, towards the second half of the 15th century, the judge Belardino de Iuliano in Solofra, in the Avellino area.

S. Vannozzi specifies that this is a patronymic surname with the sense of "son of a Giulio" (from the Latin Iulio), and documents its formal evolution through the Latinized variants De Iuliis and De Iulianis, by way of De Iuliano, down to the present form. Vannozzi records it among the oldest surnames of Cercemaggiore, in the Campobasso area, in Molise.

Rossoni describes the geographical distribution of the various forms: Iuliano is the most widespread, found along the Tyrrhenian strip from Rome to Catanzaro, throughout Campania and in Molise; Iuliani is typical of lower Molise, the Avellino area and the Foggia area; Juliano, very rare, is recorded in Campania and northern Calabria; and Juliani appears sporadically in Abruzzo, Molise and Veneto.