Wisconsin currently utilizes 6 area codes. When first established by AT&T and the Bell System in 1947, 414 covered southern and northeastern Wisconsin including Milwaukee and 715 covered northern Wisconsin. The most recently added was 534 in 2010 as an overlay to 715. Today, 715 is the most populated with an estimated 1.2 million of the state's 5.7 million residents.
Sources: North American Numbering Plan Administration (NANPA), telecom providers, and the U.S. Census Bureau.