Pennsylvania currently utilizes 13 area codes. When first established by AT&T and the Bell System in 1947, 215 covered southeastern Pennsylvania including Philadelphia, 412 covered western Pennsylvania including Pittsburgh, 717 covered the eastern half of Pennsylvania except for the Delaware and Lehigh Valleys, and 814 covered northwestern and central Pennsylvania. The most recently added was 445 in 2018 as an overlay to 215. Today, 610 is the most populated with an estimated 2.6 million of the state's 12.7 million residents.
Sources: North American Numbering Plan Administration (NANPA), telecom providers, and the U.S. Census Bureau.