A directory of U.S. area codes is available on online sites, such as Nanpa.com and MapsOfTheWorld.com. These sites provide up-to-date information about the area codes assigned in particular areas of each state.
Nanpa.com is the official website of the North American Numbering Plan Association, the agency responsible for the administration of the numbering plan resources in the United States and Canada. To access the area code directory for the United States, click Area Code Maps on the left sidebar or the image of the U.S. map on the homepage. You may choose to view the flash version or the HTML version of the U.S. area code maps. Click a state to view the area codes assigned to different areas of the state.
MapsOfTheWorld.com also provides a map of the U.S. area codes. On the homepage, hover the mouse over Utility on the top menu and click US Area Codes on the dropdown menu. The page loads a map of the United States with the states overlaid with their assigned area codes. Click a state to view a map of the state and its cities together with the assigned area codes. Alternatively, you may use the Search For US Area Code tool to find the area code for a specific state.