Merychippus was named by Leidy (1856) [also said to be 1857; numerous authors around the turn of the century put the type species in Protohippus, but this ignored priority]. It is not extant. Its type is Merychippus insignis.

It was assigned to Equidae by Leidy (1856) and Carroll (1988); to Hipparionini by Kelly (1995); and to Equinae by MacFadden (1998) and Bravo-Cuevas and Ferrusquía-Villafranca (2006).