From http://www.usmint.gov/about_the_mint/mint_facilities/index.cfm?action=PA_facilities:
The nation's first mint provides a wide array of coins and manufacturing services. Like the Denver facility, Philadelphia makes circulating coins of all denominations, commemorative coins as authorized by Congress, and produces the dies for stamping coins and medals. Philadelphia manufactures the "P" mint mark portion of the uncirculated coin sets. In addition, Philadelphia is currently the only United States Mint facility that engraves the designs of the U.S. coins and medals.
The first mint was erected at 7th and Arch Streets and by March, 1793, it delivered its first circulating coins: 11,178 copper cents. Their production was overseen by David Rittenhouse, a leading American scientist and the first Director of the United States Mint.
As the United States and its economy grew, the nation required more coins and larger Mint facilities. The mint expanded accordingly and moved three times. Its current facility, Philadelphia's fourth, opened in 1969.