The presence of populations of the Afro-Asian cyclopoid copepod crustacean Mesocyclops thermocyclopoides Harada, 1931, in southeastern Mexico and in Central America is recorded. This species was recently redescribed in detail from Old World specimens. Because of the rarity of cosmopolitan forms in Mesocyclops, neotropical records of this species were suspected to be undescribed taxa of a widespread species complex. However, it was possible, through an upgraded morphological analysis and taxonomic comparison, to confirm the occurrence of M. thermocyclopoides in the neotropics. The American specimens are described in full. In the Americas, this species seems to be distributed in Mexico and Central America only. This is the third or fourth Asian or African species of the genus that has apparently been introduced into the New World by human agency. The others are M. pehpeiensis, M. ogunnus, and M. aspericornis.