William Penn was granted the Proprietary Colony of Pennsylvania by King Charles II in 1681. The Colony was formed by parts of earlier grants to Connecticut and Virginia. It also included the original Upland county that had been established by the Swedes on the West side of the Delaware River, as noted in the another post in this timeline. This was done because King Charles granted Pennsylvania all the territory on the West side of the Delaware River, starting 12 miles north of New Castle (the portion below this line was added to New Castle County of Present day Delaware). The 3 counties of Present Day Delaware (New Castle, St. Jones and Deale) were claimed by both Pennsylvania and Maryland, but the area became known as the lower counties of Pennsylvania.
It should be noted that Proprietary Governorships were one of 4 types of colonial grants in the British Empire. The other 3 were royal, joint stock and covenant. King Charles II favored Proprietary grants to reward his allies and focus his attention on internal British Affairs. That is, the responsibility for government and economic development rested solely with the Proprietor. But, proprietorships fell out of favor as subsequent English sovereigns sought to regain full control of the colonies by establishing Royal Charters.