Here's the North American Numbering Plan Adminstration (NANPA)
This site provides information about the North American Numbering Plan (NANP) and its administration. The NANP is the numbering plan for the Public Switched Telephone Network for Canada, the US and its territories, and the Caribbean.
It's where the Area Codes come from, and lots more. Check it out.
To check which area an Area Code comes from, go here

The Long Grove, IA switchboard