"Oryzomys gorgasi" was first found in Antioquia Department of northwestern Colombia in 1967 during an expedition by the U.S. Army Medical Department and the Gorgas Memorial Laboratory. In 1971, Field Museum zoologist Philip Hershkovitz described a new species, "Oryzomys gorgasi", on the basis of the single known specimen, an old male. He named the animal after physician William Crawford Gorgas, the namesake of the Gorgas Memorial Laboratory. Hershkovitz considered the new species most closely related to "Oryzomys palustris", which at the time included North and Central American populations now divided into several species, including the marsh rice rat ("O. palustris") and "O. couesi". The species was not recorded again until 2001, when Venezuelan zoologist J. Sánchez H. and coworkers reported on 11 specimens collected in coastal northwestern Venezuela in 1992, from the Colombian locality. They confirmed that "O. gorgasi" is a distinct species related to the "O. palustris" group.