[dasv]

516 people in Spain with Farto as first surname, 485 as second surname. None with both. Quite rare. You can check distribution out yourself in a map with this neat tool from the Spanish Statistics Institute https://www.ine.es/widgets/nombApell/index.shtml

As an aside, I spent some days last week around that zone and found out about the existence of the surname Pis, which has a similar distribution and rarity, and is even more unfortunate since it means "pee" in Spanish. At least Farto is only funny in English.

Since in Spain you get your first surname from your father's first surname and your second from your mother's first that sometimes also leads to unintended hilarity in names (example, real person, Luz Cuesta Mogollón, which roughly translates to "electricity costs a bunch"!)