Area codes 317 and 463

Area codes 317 and 463 are North American Numbering Plan area codes for Indianapolis and nine surrounding counties in central Indiana. It covers all or part of Marion, Boone, Hancock, Hamilton, Hendricks, Johnson, Madison, Morgan, and Shelby counties. 317 is the original area code, while 463 is an overlay covering the same area, making ten-digit dialing mandatory for all calls in the region.

317 was one of the original area codes introduced in 1947. It originally covered the northern two-thirds of Indiana, while area code 812 served southern Indiana. In the first split of the area code system since its 1947 inception, the northern third of Indiana, including South Bend, Gary and Fort Wayne, received 219 the following year. Despite Indianapolis's rapid growth during the second half of the 20th century, and the accompanying increased number demand, this configuration remained in place for 48 years. No changes were made to 317 until February 1, 1997, when most of the old 317 territory outside of the inner ring of the Indianapolis metropolitan area switched to 765.

Wikipedia