The novel Frankenstein notes that Victor is Genevese by birth. (This means he is from or around Geneva and/or Switzerland. In his telling of his family's history, Victor states that he was born in Naples, which followed trips by his parents to Italy, Germany, and France.
Victor is very proud of his Genevese background. He states that his family is renowned in Geneva and that his ancestors have been recognized in the area for many generations as counselors and syndics (some affiliated with the court system).
Therefore, while born in Italy (Naples) which would make him Italian by birth, Victor states that he is Genevese by birthright and ancestry.