Previously undescribed fossil material from the late Eocene Hoko River Formation and the Oligocene Makah Formation, Olympic Peninsula, Washington, provides new insight into the evolution and biogeography of five families of decapod crustaceans. New taxa include Homola vancouverensis, Xeinostoma? antiqua, and Daldorfia himaleorhaphis. New material makes it possible to provide a complete reconstruction of the dorsal carapace of Macrocheira teglandi, and a possible juvenile Branchioplax washingtoniana is described for the first time. The range of the genus Homola, known in modern oceans, has been extended into the late Early Cretaceous, and the occurrence of that genus in rocks of the Pacific coast of North America marks the first authentic report of the Homolidae from that region. The Cyclodorippidae is now known to have inhabited the Pacific coast of North America as early as the late Eocene. The geologic range of the genus Daldorfia now extends into the Oligocene, and its earliest known occurrence is from rocks of Washington, U.S.A.