United States area codes for each state are mapped out below. Area codes for each state are dictated by the North American Number Plan (NANP) around the 1940s by AT&T. American phone numbers are grouped by region and assigned a Number Plan Area (NPA) number. Not every state participates in the NANP plan. It is common practice for U.S. states with higher populations to be separated into multiple Number Plan Areas such as the case with California while states like Wyoming contain only one NPA for the whole state.
When dealing with unknown callers, spam and telemarketers, looking up the phone number's area code is a good place to start. Please feel free to use this page as a quick reference when searching for information on random callers.