Area code 717

Area code 717 is a telephone area code which serves South Central Pennsylvania. The numbering plan area covers the Harrisburg, Lancaster and York metropolitan areas with a population of nearly two million people, as well as most of the area generally known as Pennsylvania Dutch Country.

717 was one of the original area codes established in 1947. The original numbering plan area (NPA) covered the eastern half of the state except for the Delaware and Lehigh valleys. It stretched from the Maryland border to the south to the New York and New Jersey borders, making it the largest of Pennsylvania's original four plan areas and the second-largest east of the Mississippi River that did not cover an entire state, after Michigan's NPA 616.

Despite the presence of five of the state's 15 largest cities (Harrisburg, Lancaster, York, Scranton and Wilkes-Barre), this part of Pennsylvania is not as densely populated as the Delaware and Lehigh Valleys. As a result, for the next 41 years, 717 was the largest numbering plan area on the Eastern Seaboard. It was pushed slightly eastward in 1994 as part of the split of Philadelphia's area code 215, when a number of outer Philadelphia suburbs that were slated to transfer to area code 610 were instead shifted to 717. These areas were served by non-Bell telephone companies who wanted to consolidate their eastern Pennsylvania customers into a single area code.

...
Wikipedia