The Welsh Tract, also called the Welsh Barony, was a portion of the U.S. state of Pennsylvania settled largely by Welsh-speaking Quakers. It is located to the west of Philadelphia. The original settlers, led by John Roberts, negotiated with William Penn in 1684 to constitute the Tract as a separate county whose local government would use the Welsh language. The Barony was never formally created, but the many Welsh settlers gave their communities Welsh names that survive today. A more successful attempt at setting up a Gwladfa (Welsh-speaking colony) occurred two centuries later, in the Chubut Province of Patagonia, Argentina.
In the late 17th century, there was significant Welsh emigration to Pennsylvania for religious and cultural reasons. In about 1681, a group of Welsh Quakers met with William Penn to secure a grant of land in which they could conduct their affairs in their own language. The parties agreed on a tract covering 40,000 acres (160 km²), to be constituted as a separate county whose people and government could conduct their affairs in Welsh. The Welsh Tract's boundaries were established in 1687, but notwithstanding the prior agreement, by the 1690s the land had already been partitioned among different counties, despite appeals from the Welsh settlers, and the Tract never gained self-government.
The Roberts and other Welsh families became influential in the area, through the building of mills and the eventual introduction of the railroad. It is the railroad that gives the best-known part of the area its current name — the Main Line, named after the mainline of the Pennsylvania Railroad, now absorbed into Amtrak as the principal intercity passenger line of the east coast. After the American Civil War, 104 Welsh families from this region migrated to Knoxville, Tennessee, establishing a strong Welsh presence there.