Either don't mention it at all or mention it fairly early. The reader is capable of building a decent image of the location in their mind and it's fine both for real locations and (even easier) for imaginary/undefined ones. That doesn't really matter. What matters is not to force them to break it down. It's extremely frustrating for a reader to build an imaginary location of imaginary land in their mind and then have it utterly shattered by the author revealing a common piece of knowledge conflicting with that image later on.
Sure if the revelation is the essential secret, it might be interesting; there are stories that tell a sequence of events creating a very simple, straightforward and obvious point of view, and then flip everything upside down by one simple revelation at the end where suddenly you realize the protagonist was one of the monsters, or that the story is not about horrible events from times long past but contemporary and about real events that take place now.
But if the revelation is not ground-breaking but significant, for example suddenly solidifying the world from "abstract European country" to "Italy" when the reader made up a decent image of the location, not quite conforming to the image of Italy, that's a very unpleasant experience.
Related: Is the ambiguity in my story the salt which makes it tasty or just plain frustrating? - see my answer to that question too; in essence that story is very frustrating by dripping new facts all along, making us reshape whatever image we've built over and over.