Museum specimens and published literature records were examined to determine how many taxa of freshwater mussels of the family Unionidae occurred within the boundaries of the State of Mississippi. Eighty nine taxa (85 described species, two of which have two described subspecies within the state; two undescribed species) were found to be distributed over the 10 river drainages within the state. The greatest number of taxa was found in the Tombigbee River drainage (52), followed by the Yazoo River drainage (46), and the Pearl River and the Big Black River drainages (39). The Coastal Rivers drainage, those streams draining into the Gulf of Mexico between the Pearl River and Pascagoula rivers, had the fewest with only six documented species. Almost half of the freshwater mussel taxa in Mississippi are considered imperiled, and 10 species appear to have been extirpated from the state.