The results of over 100 years of inventory work on the Lepidoptera of Plummers Island, Montgomery County, Maryland, U.S.A., were summarized recently in a volume dedicated to the invertebrate fauna of that site. That work documented a cumulative total of 836 species of Lepidoptera. To that list I add 20 species: Niditinea sabroskyi Metz, Davis & Davis, 2018 (Tineidae), Tinea carnariella Clemens, 1859 (Tineidae), Tinea apicimaculella Chambers, 1875 (Tineidae), Elachista illectella (Clemens, 1860) (Elachistidae), Pseudocherlaria walsinghami Dietz, 1900 (Gelechiidae), Coleotechnites thujaella (Kearfott, 1903) (Gelechiidae), Coleotechnites quercivorella (Chambers, 1872) (Gelechiidae), Trypanisma prudens Clemens, 1860 (Gelechiidae), Abrenthia cuprea Busck, 1915 (Glyphipterigidae), Argyresthia oreasella Clemens, 1860 (Argyresthiidae), Aethes terriae Sabourin & Miller, 2002 (Tortricidae), Aethes razowskii Sabourin & Miller, 2002 (Tortricidae), Aethes sexdentata Sabourin & Miller, 2002 (Tortricidae), Aethes mymara Razowski, 1997 (Tortricidae), Aethes promptana (Robinson, 1869), (Tortricidae), Spinipogon resthavenensis Metzler & Sabourin, 2002 (Tortricidae), Clepsis listerana (Kearfott, 1907) (Tortricidae), Gretchena amatana Heinrich, 1923 (Tortricidae), Rhopobota finitimana (Heinrich, 1923) (Tortricidae), and Exelastis pumilio (Zeller, 1873) (Pterophoridae). Ten of the species are represented by historical records that previously were overlooked, the other 10 species have been collected since 1998.