Reithrodontomys mexicanus (Saussure, 1860) is a cricetid rodent commonly called the Mexican harvest mouse and is one of 24 recognized species in the genus. It has grooved upper incisors distinctive of Reithrodontomys, and a medium to relatively large size, with tail longer than head and body; dorsal pelage varies from brown to cinnamon orange. It is distributed from Mexico to Nicaragua and in the northwestern region of South America. It occupies different habitats including humid pine-oak forests, cloud forests, and deciduous forests at elevations from about 1,000 to 3,800 m. R. mexicanus is listed as “Least Concern” by the International Union for Conservation of Nature and Natural Resources, although information about population size throughout its distribution range is unknown.