Karns is an unincorporated community in Harrison Township, Allegheny County, Pennsylvania, United States; it is located in Western Pennsylvania within the Pittsburgh Metropolitan Statistical Area, approximately 24 miles northeast of Pittsburgh. Karns is situated along the Allegheny River at Pool 4 across from Jacks Island just above Lock and Dam 4 between Natr…Karns is an unincorporated community in Harrison Township, Allegheny County, Pennsylvania, United States; it is located in Western Pennsylvania within the Pittsburgh Metropolitan Statistical Area, approximately 24 miles northeast of Pittsburgh. Karns is situated along the Allegheny River at Pool 4 across from Jacks Island just above Lock and Dam 4 between Natrona, Natrona Heights, and Sligo. The elevation of Karns is 817 feet above sea level.