Derry Township is a township in Dauphin County, Pennsylvania, United States. The population was 21,273 at the 2000 census. Hershey, Pennsylvania, the site of the well-known Hershey's chocolate factory and its affiliated amusement park, are located within the township. Pennsylvania State University's Milton S. Hershey Medical Center and the Penn State Hershey Children's Hospital are also located on a large tract of land in the township.