Photuris potomaca Barber is a rare firefly species for which few accounts exist in the scientific literature. Those that do occur are limited in scope and lack detailed habitat descriptions. Additionally, there are no confirmed records of this species since 1978. To determine whether the species is still extant, 11 sites near historical observations along the upper reaches of the Potomac River and its tributaries in West Virginia (n = 10) and Maryland (n = 1), USA were surveyed during 2022, and 14 additional sites were surveyed during 2023 in river basins adjacent to the Potomac River in West Virginia. A secondary objective was to provide more detail on the species' morphology, flash pattern, and habitat associations. We found populations at nine locations within this species' historical watershed of the Potomac River in West Virginia and Maryland, and four locations in the Monongahela River basin of West Virginia where it had not been previously reported. Sites with populations of P. potomaca were characterized by early successional riverside habitat containing cobblestone beaches, driftwood, and sapling American sycamores (Platanus occidentalis L.; Platanaceae). Several of these sites are consistent with the recently classified and highly threatened “riverscour” ecosystems, thereby providing the first association of P. potomaca with a distinct ecosystem type. Photuris potomaca not only persists in the Potomac River basin but can also be found in scattered locations in the Monongahela River basin where it can be locally common. Inventory for P. potomaca should target unsurveyed riverscour ecosystems throughout the southeastern United States.