The surname Oneto is of toponymic origin and is linked with places of the Ligurian and Piedmontese sphere. On this point E. Rossoni and P. Regati agree, noting that it probably derives from place names such as the Piani d'Oneto (in the Imperia area) or from the Oneto torrent in the Genoa area, used to indicate the geographical provenance of the line.

Both authors document its presence from the 14th century, linked to movements from Piedmont towards Liguria, which would explain its rootedness in this region. Along the same lines, P. Regati rules out a possible derivation from the term oneto (related to alneto, "alder wood"), thus reinforcing the toponymic interpretation as the most probable in the origin of the surname.