The authors agree that this is a surname of toponymic origin, widely diffused throughout Italy. It derives from the Latin valles, which designates both a place surrounded by mountains and, in some regions, a marshy zone or a river or torrent. The surname is linked to the numerous place names containing the root vall, such as Vallebuona, Vallebona, Vallese, Valletta, Vallo, Vallone and others, present in different parts of the Italian peninsula.

F. Miranda notes that the surname is diffused mainly in northern Italy —Liguria, Piedmont, Lombardy, Veneto— with a consistent nucleus in Lazio and Campania, and smaller presences in Friuli-Venezia Giulia, Trentino-Alto Adige, Emilia-Romagna and Tuscany. In Sicily it appears in zones of Catania, Enna, Messina, Palermo and Ragusa.

F. De Laurentiis highlights that the greatest frequency is recorded in Liguria, and notes that the term valle took on specific regional meanings in some zones, such as "river", "torrent" or "marshy zone", which broadened the range of place names that could have given rise to the surname.

E. De Stefani provides details about the presence of the surname in Friuli, where it is documented from the beginning of the 16th century in localities such as Meduno, Tolmezzo, Ovaro, Sutrio and Enemonzo. The first attestations with the preposition de —in forms such as de Val or de Valle— confirm the toponymic origin and allow a possible derivation from the personal name Valent to be ruled out. In the Forni Avoltri area, especially in the locality of Sigilletto, the Friulian dialectal form Di Val is preserved, also documented as Dival (without a space). De Stefani also mentions the surname Vallaro, with its own derivative suffix, attested in Tramonti and Meduno, as a kindred form with an independent distribution.