Township municipal offices are located at 15 West Mill Street, Yaegertown PA 17099; phone 717-248-8151.
Derry Township, the oldest in the county and at one time including the entire county, was erected by the court of Cumberland County more than twenty years before Mifflin County was organized. In August 1754, about a month after the purchase of the lands in the Juniata Valley from the Indians, Cumberland County organized four townships "other side of the North Mountain." These townships were Fannet, Aire, Tyrone and Lack. Early in 1767 a petition was presented to the court by the settlers north of the Juniata, asking for the erection of a new township in that district, and at the July term the court defined the boundaries of Derry Township as follows: "Beginning at the middle of the Long Narrows; thence up the north side of the Juniata as far as Jack's Narrows; thence to include the valleys of the Kishacokulus and Jack's creek."
The boundaries as thus established embraced all that portion of the present county of Mifflin lying north of the Juniata, River and part of what is now Brady Township in Huntingdon County. Just when that portion of Mifflin County south of the Juniata was taken into the township is not shown by the records, but when the assessment of 1768 was made the names of the people living in that territory were included, so it is probable that it was annexed soon after the township was organized. The names of seventy land owners and over 25,000 acres taken up on land warrants were included in the assessment rolls for that year. One of the earliest settlers on the Kishacoquillas Creek, on the southside of Jack's Mountain, was Everhart Martin, whose first land warrant was dated April 2, 1755. Later he entered several other tracts, a part of which became the property of the Freedom Iron Company and later of the Logan Iron and Steel Company. However, it is not certain that he ever lived upon the lands thus entered in his name. His son, Christopher, built a saw-mill on the creek opposite Yeagertown at an early date. Samuel Holliday came to what is now Bratton Township, in 1755. He located on the Juniata, near the present borough of McVeytown, where he built a grist-mill, which was probably the first one in Derry Township, and was built about the time the township was organized. Before the purchase of the lands from the Indians in 1754, Robert Buchanan located a trading post at the mouth of the Kishacoquillas Creek, where the borough of Lewistown now stands. When the French and Indian war began he removed to Carlisle and did not return to his trading post until about 1762. In July, 1762, he took out a warrant for 201 acres of land "lying on the northwest side of the river and extending above the mouth of the Kishacoquillas Creek." Warrants were taken out at the same time for land in the vicinity by his son and his daughter, the former for ninety-six and the latter for two-hundred and eighteen acres. On August 2, 1766, John Early took up part of the land where the village of Kelleyville was afterward built. John Rothrock, before the Revolution, settled four miles northeast of Lewistown. George Rothrock settled in Ferguson valley in 1773. Matthew and George Kelly settled in the south end of the Dry Valley and received warrants for their lands October 1, 1776. Robert Forsythe came in 1784 and afterward became one of the pioneer merchants of Lewistown. Andrew Gregg took up a tract below that of Jane Buchanan in 1787, and two years later was appointed one of the trustees to organize Mifflin County. John Alexander also came in 1787 and purchased a large tract of land in Little valley. In 1788 Ulrich Steely entered one-hundred acres on the south side of Jack's Mountain. On March 9, 1790, James Mayes took out a warrant for two-hundred and fifty acres near the present village of Yeagertown. His brother Andrew took up a large tract of land in the same neighborhood in 1792. In 1793 Philip Minehart was operating a saw-mill in that part of Derry afterward cut off to form Granville Township, and in 1794 Joseph Strode built a grist and saw-mill on Brightfield's run. Settlers continued to come in before the close of the century, and in 1800 the population of the township was 1135.