The Lackawanna River begins at the confluence of the East Branch Lackawanna River and the West Branch Lackawanna River in Stillwater Lake in Clifford Township, Susquehanna County. It flows south-southeast for a few miles in a deep valley, crossing Pennsylvania Route 171 and passing through Forest City. The river then enters Clinton Township, Wayne County. Here, it flows south for more than a mile before turning southeast for several tenths of a mile. It then turns south-southwest for a few miles, meandering into Vandling, in Lackawanna County. The river only flows through Vandling for a few tenths of a mile before entering Fell Township. The western side of its valley becomes steeper again and the river continues meandering south-southwest for a while before turning west for several tenths of a mile and into Simpson, where its valley broadens again. In Simpson, it turns southwest and crosses Pennsylvania Route 171 again before receiving the tributary Wilson Creek from the .