A new species of Eupsilia Hübner phenotypically allied to E. cirriplaea (Franclemont, 1952) and E. sidus (Guenée, 1852) is described from northeastern North America. Identification of E. schweitzeri, n. sp., is most reliably made on the basis of larval morphology or genetic data, although most adults can be determined using subtle forewing features, including their derived forewing scale type. The adult, genitalia, forewing scales, and larvae of the new species are illustrated. Keys are provided to adults and larvae of the seven northeastern Eupsilia. Eupsilia walkeri (Grote, 1864) is synonymized under E. vinulenta, n. syn. Scopelsoma colorado (Smith, 1903) is removed from synonymy with Eupsilia sidus and given valid species status as Eupsilia colorado, rev. stat., and a neotype is designated for E. sidus.