Counties formed since 1775

Allegheny - formed 1788 from part of Westmoreland and Washington

Dauphin - formed 1785 from part of Lancaster

Delaware - formed 1789 from part of Chester

Fayette - formed 1783 from part of Westmoreland

Franklin - formed 1774 from part of Cumberland

Huntingdon - formed 1787 from part of Bedford

Luzerne - formed 1786 from part of Northumberland

Mifflin - formed 1789 from part of Cumberland and Northumberland

Montgomery - formed 1784 from part of Philadelphia

Washington - formed 1781 from part of Westmoreland