Species occurrences of darkling beetles (Coleoptera: Tenebrionidae) are listed for the historically collected locality of Plummers Island, Maryland, on the Potomac River just upstream from Washington, D.C. The list is compared to that of the currently known Maryland species, which includes a number of new state records and range extensions. Notes on some of these occurrences and the absence of certain species are discussed. Maryland records from multiple sources now total 128 species of this family of insects. Plummers Island records, from the beginning of the 20th century to the present, include nearly 50% of the state's fauna, and an additional 25% of the state's tenebrionids are expected there.