Four new species of MacrelmisMotschulsky, 1860 are described from the southwestern United States and northern Mexico: Macrelmis harleyi Barr, new species from Arizona, Macrelmis mexicana Barr, new species from Mexico, Macrelmis shepardi Barr, new species from Arizona, New Mexico, Texas, and Mexico, and Macrelmis texangusta Barr, new species from Texas and Mexico. Photographic images illustrate the external morphology and male genitalia of the new species, as well as that of Macrelmis shoemakei (Brown, 1971), Macrelmis moesta (Horn, 1870), and Macrelmis texana (Schaeffer, 1911), which occur in the same geographic region. The genitalia of M. moesta and M. texana are described and illustrated for the first time. A key to the 14 known species of Macrelmis occurring in the southwestern United States and Mexico is provided, accompanied by line illustrations of the genitalia of the remaining seven Mexican species not included in the species treatments. Also included are geographic distribution maps for the seven species that are discussed in this article.