Tredyffrin Township is a township located in eastern Chester County, Pennsylvania, United States. Originally settled in the late 17th century, Tredyffrin is bounded by Delaware and Montgomery counties. It includes on its northern boundary a small part of Valley Forge National Historical Park, where George Washington encamped during the American War of Independence. Tredyffrin and the entire Great Valley region also have many limestone deposits. Unincorporated communities within Tredyffrin Township include Chesterbrook, Strafford, a portion of Paoli, and a portion of Wayne. Tredyffrin is bordered by Easttown, East Whiteland, Willistown, Charlestown, Upper Merion, Radnor and Schuylkill townships.
The rocks of Tredyffrin were laid down in the upper Paleozoic, meaning that they are primarily metamorphic. Limestone is often at the surface in the Great Valley, so many limestone kilns were created in the 18th century. The northern edge of the township is a ridge of quartzite and sandstone (the Cambrian Chickies Formation) including Valley Forge Mountain (or Mount Misery), which was mined for quartz in the 18th century through the mid-19th century.
Historic Buildings in Tredyffrin Township include County Bridge No. 171, Cramond, Cressbrook Farm, Federal Barn, Great Valley Mill, Greenwood Farm, David Harvard House, Lafayette’s Quarters, Maj. Gen. Lord Stirling Quarters, Strafford Railroad Station, Valley Forge National Historical Park, Joseph Walker House, and Wetherby-Hampton-Snyder-Wilson-Erdman Log House are listed on the National Register of Historic Places. In addition, the Wharton Esherick Museum is listed as a National Historic Landmark; it was built starting in 1926, Historic Waynesborough.