Counties formed since 1790

Adams - formed 1800 from part of York

Armstrong - formed 1800 from part of Allegheny, Westmoreland and Lycoming

Beaver - formed 1800 from part of Allegheny and Washington

Butler - formed 1800 from part of Allegheny

Centre - formed 1800 from part of Mifflin, Northumberland, Lycoming and Huntingdon

Crawford - formed 1800 from part of Allegheny

Erie - formed 1800 from part of Allegheny

Greene - formed 1796 from part of Washington

Lycoming - formed 1795 from part of Northumberland

Mercer - formed 1800 from part of Allegheny

Somerset - formed 1795 from part of Bedford

Venango - formed 1800 from part of Allegheny and Lycoming

Warren - formed 1800 from part of Allegheny and Lycoming

Wayne - formed 1798 from part of Northampton