The myrmecophilous Paederinae rove beetle genus Megastilicus Casey, 1889 from North America is reviewed based on museum specimens. Prior to this study, the genus was monotypic with one species Megastilicus formicarius Casey, 1889 described. Here, we provide a redescription of the genus and the type species, designate a lectotype, and provide pictures of habitus and illustrations of the aedeagus and genital segments. Additionally, we describe a new species for the genus, Megastilicus iowaensis sp. nov., include an identification key to the two species and present the distribution map of both of them, including new state records. We discuss the assignment of the genus to the subtribe Stilicina based on morphological features.