The authors agree that this surname derives from the place name Ganna or Valganna, a locality of the province of Varese, in the region of Lombardy.

E. Rossoni adds that the name Ganna was in use among the Gaulish Senones, a people of antiquity, among whom a mother and seer called Ganna is remembered. He also notes that the transformation into a surname has documentary traces from the 9th century, in a deed of the Lombard period that mentions a certain Iohanni qui vocatur Ganna episcopus. The surname is peculiar to the Varese area.