On March 13, 1684,
William Penn decided to set aside a portion of what was then the
Province of Pennsylvania for settlements for
Welsh immigrants. This area, known as the "
Welsh Tract", was surveyed in 1684 and included several modern-day townships, including Tredyffrin. Although the Welsh Tract was originally meant to be a self-ruling municipality, it was divided between Chester County and
Philadelphia when that county was created in 1685, and the Welsh subsequently submitted to the authority of Chester County. In 1707, Tredyffrin was incorporated as a township. This name comes from the Welsh
tre(f), which means "town", joined to
dyffryn, which means "wide, cultivated valley". Tredyffrin was quick to develop into a thriving township. In 1710, the first mill in Tredyffrin was started by Thomas Jerman on what is now North Valley Road. Swedesford Road, one of the first roads in the township, was created by 1718. As the population of the township grew, with 30 resident landowners in 1722 and 83 in 1774,
churches sprung up to meet the demand by religious residents. In 1710, the
Baptist minister Hugh Davis moved to the Great Valley from Britain and, there being several Baptist families in this area, the
Baptist Church in the Great Valley was formed on April 22, 1711. The church originally met in
Radnor. However, there were enough members of this Baptist church that by 1722, a log building was erected in Tredyffrin to serve the congregation. As Tredyffrin includes part of
Valley Forge National Historical Park, there are many
Revolutionary War-related sites in the township, especially the park and houses where various generals were quartered. Development in the township was sparked in the 19th century by construction and advertisement of the "Main Line" railroad service, which terminated in
Paoli, which straddles the western border of the township. Tredyffrin-Easttown school district was unusual for the area in being
racially integrated during the early part of the century. In 1932, the district planned to segregate after building a new school, and African Americans in the township boycotted the school system for two years in protest (the "School Fight"). In 1934 a negotiated settlement was reached whereby the schools remained integrated, and helped kill school segregation in Pennsylvania. During the
Cold War, a
Nike anti-aircraft missile site was active in the township. It was located off Le Boutillier Road, near Swedesford Road. == Historic buildings ==