Chester County was one of the three original Pennsylvania counties created by William Penn in 1682. It was named for Chester, England. It is part of the Delaware Valley region and is the only Delaware Valley county in Pennsylvania that does not actually border Philadelphia. The original Chester County seat was the city of Chester, a center of naval shipbuilding. But, it became part of Delaware County when that county was formed from the eastern portion of the Chester County on September 26, 1789. West Chester was designated as the new county seat that year, and has remained so.  Much of the history of Chester County arises from its location between Philadelphia and the Susquehanna River. The first road to "the West" (meaning Lancaster County) passed through the central part of Chester County; with some re-alignments, it became the Lincoln Highway and later U.S. Route 30. This road is still named Lancaster Avenue in most of the Chester County towns it runs through. The first railroad (which became the Pennsylvania Railroad) followed much the same route, and the Reading Railroad progressed up the Schuylkill River to Reading. Industry tended to concentrate along the rail lines. Easy transportation allowed workers to commute to urban jobs, and the rise of the suburbs followed. To this day, the developed areas form "fingers" extending along major lines of transportation. The Battle of Brandywine was fought at what is now the southeastern fringe of the county, and the Valley Forge encampment was at the northeastern edge. The former Valley Forge Army Hospital, constructed during World War II, was one of the largest military hospitals in the United States.