Galecyon is one of the first appearing hyaenodontid creodonts, as well as one of the most poorly known. New specimens greatly improve our understanding of the morphology of this early Eocene genus, thereby enhance knowledge of the earliest radiation of Hyaenodontidae, and include the first associated upper dental remains, as well as fragmentary cranial remains. The new records substantially expand the stratigraphic range of the genus and allow recognition of two new species. The first, Galecyon peregrinus n. sp., is a small, early species that includes the first records of Galecyon from the earliest Eocene Wa-0 interval. The second, Galecyon chronius n. sp., is a large, terminal species, represented by numerous specimens that extend the range of the genus into the late Wasatchian. The type species, G. mordax, is restricted to specimens that are intermediate in size and stratigraphic position. Phylogenetic analysis of early hyaenodontids confirms the monophyly of Galecyon and places it basal to Prolimnocyon, Prototomus, and Pyrocyon. Arfia is identified as the earliest diverging hyaenodontid sampled, contrasting with prior support for a more crownward position. Prototomus martis is more closely allied to Pyrocyon than to other species of Prototomus. The three North American species of Galecyon form a probable anagenetic lineage.