A floristic survey of Lauderdale County, Mississippi was undertaken from the spring of 2004 through the fall of 2009 in order to document the flora and describe plant communities from this poorly studied region within Mississippi. A total of 1175 vascular plant species (1206 taxa altogether, including species and infraspecific taxa) was recorded from the county. Oenothera sinuosa and Geranium molle were collected for the first time in the state of Mississippi, and Carex breviculmis was recorded from North America for the first time. One hundred and eighty-six introduced species were recorded in the county. Forty-seven rare and uncommon species, according to the Mississippi Natural Heritage Program special plant tracking and watch lists, were recorded from Lauderdale County and many range extensions and species disjunctions were discovered. We describe nine primary plant communities in the county and discuss the biogeographical importance of the flora of Lauderdale County relative to the rest of the state.