[2] The township includes the Three Mile Island Nuclear Generating Station, the location of the largest accident in the history of the American nuclear power generating industry, which took place in 1979.

Since the township was so large and difficult to govern, the residents petitioned the court in 1767 to subdivide the land into two parts, the eastern section to remain Derry and the western to be Londonderry.

[4] Derry and Londonderry became a part of Dauphin County when it was established in 1785.

[6] As of the census[8] of 2000, there were 5,224 people, 2,004 households, and 1,517 families residing in the township.

There were 2,095 housing units at an average density of 92.0 per square mile (35.5/km2).

20.6% of all households were made up of individuals, and 7.8% had someone living alone who was 65 years of age or older.