The surname Ongaro is of ethnic origin and derives from the medieval names and nicknames Ongaro or Ungaro, used to indicate a person "belonging to the Hungarian people" or coming from Hungary. On this point E. De Felice and F. De Laurentiis agree, noting that it is a demonym transformed into a surname, in line with a common practice in Italian onomastics.

Both authors highlight that this type of designation spread in northern Italy between the 11th and 12th centuries, in a historical context marked by incursions and settlements of Hungarian groups in different regions, especially in Piedmont and the north-east. In this way, the surname reflects an origin linked to the geographical or ethnic identification of the founding ancestor.