The Waterloo Wildlife Research Station (WWRS) is a 505 ha state-owned research area located in the mixed mesophytic forest region of unglaciated southeastern Ohio. The vascular flora of WVVRS was inventoried from March 1997 to October 1999. The objectives of this study were to survey the composition and distribution of native and non-native plant species across natural and managed habitats at WWRS and to document the presence of threatened and endangered species. A total of 559 species in 323 genera and 109 families were located within seven plant community types. This survey adds 241 new species to a 1955 floristic survey of WWRS, resulting in 655 species in 362 genera and 114 families. This total includes two state endangered, two state threatened, and six potentially threatened species. Twenty percent of the species are non-native to the eastern United States, occurring primarily in anthropogenically disturbed habitats.