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 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.
[1][2]Whereas diverse considerable persons among the Welsh Friends have requested me that all the Lands Purchased of me by those of North Wales and South Wales, together with the adjacent counties to them, as Herefordshire, Shropshire and Cheshire, about forty-thousand acres, may be laid out contiguously as one Barony, alledging that the number already come and suddenly to come, are such as will be capable of planting the same much within the proportion allowed by the custom of the country, and so not lye in large useless vacancies.
And because I am inclined and determined to agree and favor them with any reasonable Conveniency and privilege: I do hereby charge thee and strictly require thee to lay out the said tract of Land in as uniform a manner as conveniently may be, upon the west side of Schuylkill river, running three miles upon the same, and two miles backward, and then extend the parallel with the river six miles and to run westwardly so far as this the said quantity of land be Completely surveyed unto you.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.
As suburbanization spread westward from Philadelphia in the late 19th century (thanks to the railroads), living in a community with a Welsh name acquired a cachet.