History
Captain John Smith first discovered Prince William County during an expedition up the Potomac River in 1608. Smith found the region inhabited by Anacostan, Doeg, Iroquois, and Piscataway Indians. The first known colonial settlement was founded in 1722. In 1730, the Virginia General Assembly carved out an area approximately 2,000 square miles in size and named it Prince William County, after the second son of England’s King George II. At that time Prince William County comprised all of “Northern Virginia” but by 1759, the General Assembly substantially reduced the County’s size. Fairfax County was formed in 1742 and Fauquier County was formed in 1759, both from the original Prince William County area.In 1730, the Dumfries area was prominent in the County and may have been the location of an official Tobacco Inspection Station due to its close proximity to the Potomac River. This is important because the Potomac River was a major regional route used to export tobacco to England, which was profitable for the southern colonial regions. The Tobacco Inspection law, passed in Virginia in 1730, required all exported tobacco shipments to bear an inspection certificate. Dumfries officially became a town in 1749 and in 1763 it reached an economic milestone by exporting more tobacco tonnage than the colony of New York
Source: History of Prince William County at pwcorg.gov