In an SBS question, a fan asked if the Straw Hats were real, what nationality would they be of. Based on their appearances, Oda gave his answer.
D: “Oda-sensei, I have a question. If One Piece was set in the real world, which countries would the nine Straw Hats come from?”
Oda: “Well. I’ll just put what fits with the character’s image.”
Luffy: Brazil
Zoro: Japan
Nami: Sweden
Usopp: Africa
Sanji: France
Chopper: Canada
Robin: Russia
Franky: USA
Brook: Austria
Jinbe: India
The whole crew is supposed to have roots from different heritages. Interestingly the only Straw Hat Member who is inherently Japanese is Zoro. Curiously enough, Usopp doesn’t get his own nationality, but instead we have to guess where in the continent of Africa he might be from—maybe he’s South African?