American Eel Anguilla rostrata populations along the Atlantic coast of the United States have been in decline over the past several decades. One suggested cause of the decline is construction of barriers that block access to upstream tributaries where they can spend a significant portion of their lives. Success of reintroduction efforts above barriers has rarely been evaluated. Within the Susquehanna River (Chesapeake Bay watershed), over 1 million eels were released above four major downstream barriers in the past decade. We used backpack electrofishing and tagging to monitor growth, sexual differentiation, and population density of reintroduced eels in Buffalo Creek, a tributary to the Susquehanna River (Pennsylvania). From 2012 to 2019, we caught over 2,000 individuals, tagged more than 1,800, and recaptured 229. Recaptured eels provided insight into growth, sexual differentiation, and movement. Nearly 99% of recaptures remained near stocking locations. The average growth rate was 47.8 mm/y and ranged between −5.8 and 116.0 mm/y. Females generally grew significantly faster than males, and growth rates of several females exceeded 100 mm/y, a rate typically associated with estuarine residents. The population density within stocking sites was over 2,300 eels/km, roughly four times higher than Susquehanna River tributaries below the most downstream dam, and exceeded the target stocking goal of 529 eels/km. While we caught most eels in areas sampled near stocking locations, we captured some eels in smaller upstream tributaries away from stocking locations. Our study is the first to examine how reintroduced eels grow following stocking above four major dams on the Susquehanna River. We suggest that managers considering moving eels above blockages account for release location and density to achieve desired benefits to the overall population.