Тhe agromyzid (Diptera: Schizophora: Agromyzidae) fauna of America north of Mexico is described in the first part of this publication, including a genus key and discussions on morphology, life history and classification. The second part is a species-level revision of the family in the “Delmarva” states of the United States of America, that is, of the District of Columbia and the surrounding states of Delaware, Maryland, Virginia and West Virginia. The fauna of this region includes 156 species.This study presents 346 new state and provincial records and 23 new country records, two of which are new continental records (Agromyzaabiens Zetterstedt and A.apfelbecki Strobl). Liriomyzaendiviae Hering is no longer considered to occur in North America. Fifteen species are newly described: Agromyzaechinalissp. nov., Melanagromyzabrunkeisp. nov., M.eoflacensissp. nov., M.glyptossp. nov., M.rutellasp. nov., Ophiomyiacapitoliasp. nov., O.cupreasp. nov., O.galiodessp. nov., O.heleiossp. nov., O.kaliasp. nov., O.laticolissp. nov., Cerodontha (Poemyza) ungulasp. nov., Phytomyzaavicursasp. nov., P.catenulasp. nov., and P.winklerisp. nov. Four new species-level synonyms and one genus-level synonym are provided: Agromyzamarmorensis Spencer syn. nov. is included as a synonym of A.aristata Malloch; Melanagromyzafastosa Spencer, syn. nov. is included as a junior synonym of Ophiomyiatiliae (Couden); Melanagromyzaverbesinae Spencer is considered a synonym of M.vernoniana Steyskal; Phytomyzaranunculoides Spencer, syn. nov. is included as a junior synonym of Phytomyzaloewii Hendel; the genus Liomycina Enderlein, syn. nov. is included as a junior synonym of Phytobia Lioy. Ophiomyiaultima (Spencer), comb. nov. is recombined from Melanagromyza. Euhexomyzaalbicula Spencer, stat. reinst., comb. nov. is resurrected from synonymy with E.winnemanae (Malloch). New host records are given.