The endangered Ozark big-eared bat (Corynorhinus townsendii ingens) is currently found in north-central and northwestern Arkansas and northeastern Oklahoma. Although historically known to be present in 2 counties on the southwestern border of Missouri, this species has not been observed in Missouri since 1971. A female Ozark big-eared bat specimen in the museum collection of Harvard University was reportedly collected in Arkansas, possibly in 1858. An investigation of the documentation associated with this and other specimens collected by the same individual suggests that this Ozark big-eared bat may have been collected on the Osage River in west-central Missouri in 1853. Another early naturalist reported the presence of what may have been Ozark big-eared bats in this general vicinity in 1854, providing additional support for their potential presence along the Osage River in Missouri at this time. Taken together, these historic reports suggest that the Ozark big-eared bat may have been present throughout the entire Missouri Ozarks during the mid-1800s and that a significant contraction of this species' range has occurred since then.