In the first Harry Potter book, Hagrid tells Harry that Gringotts is the only bank:
‘They didn’ keep their gold in the house, boy! Nah, first stop fer us is Gringotts. Wizards’ bank. Have a sausage, they’re not bad cold – an’ I wouldn’ say no teh a bit o’ yer birthday cake, neither.’
‘Wizards have banks?’
‘Just the one. Gringotts. Run by goblins.’
Harry Potter and the Philosopher's Stone, Chapter 5: Diagon Alley.
In the second one, we learn that Gringotts has people working in others places of the world:
Bill was the oldest Weasley brother. He and the next brother, Charlie, had already left Hogwarts. Harry had never met either of them, but knew that Charlie was in Romania, studying dragons, and Bill in Egypt, working for the wizards’ bank, Gringotts.
Harry Potter and the Chamber of Secrets, Chapter 4: At Flourish and Blotts.
It has been suggested on this very website that there is probably more than one currency in Harry Potter's wizarding world: Are the wizard coins in the Harry Potter books international?. (Personally, I'm of the opinion that Rowling used a hyperbole in the passage discussed in that question).
So, was Hagrid exaggerating? Was he referring just to the United Kingdom? Is Gringotts really the one and only bank on Earth? And, more importantly, is there any canon answer that supports either hypothesis?
Possible answer: https://scifi.stackexchange.com/a/50088/23401