What is what area code is 628?

Area code 628 is an overlay code for parts of California. This means it was added to an existing area code (or area codes) to handle increased demand for phone numbers. It doesn't cover a geographically distinct area on its own; rather, it serves the same general region as the area codes it overlays. Calls within the same geographic region may be between 628 and other area codes in that region. You need to know the specific number to know its precise location.