The Elachista tetragonella group is redefined, its limits extended to include the genus Biselachista Traugott-Olsen & Nielsen, 1977. The North American species of the tetragonella group are described and illustrated, and a key is given to the males. 19 species are recognized in the Nearctic region, including 12 new species: Elachista pyrrha (Alberta), E. absaroka (Wyoming), E. calusella (Florida), E. beothucella (Newfoundland), E. glenni (Illinois), E. cerasella (Nebraska), E. serra (Labrador), E. huron (Quebec), E. vinlandica (Newfoundland), E. ciliiyera (Mississippi), E. lenape (New Jersey) and E. pelaena (California). The male of E. inaudita Braun and the female of E. leucosticta Braun are described for the first time. Elachista eleochariella Stainton and E. albidella Nylander (= E. tanyopis Meyrick, syn. n.) are recognized as Holarctic species.