Ethmia umbrimarginella is a moth in the Depressariidae family. It is found in southern Arizona and New Mexico in the United States. The length of the forewings is 9.5-9.7 mm. The ground color of the forewings is dark slate gray. The immediate costal edge is dirty white up to the distal one-fourth. The ground color of the hindwings is white, with a broad dark gray margin around the apical, terminal and dorsal areas. Adults have been recorded in February.