The giant floater is a widespread species, found throughout te Mississippi and Missouri river drainages, the St. Lawrence drainage,, Gulf of Mexico through Louisiana and Texas. In Canada it is in the Interior basin from western Ontario to Alberta.
In Michigan, Pyganodon grandis is found throughout streams, lakes and rivers in the state. In general, it is more common in lakes, but is widespread throughout river systems. (Burch, 1975)
- Burch, J. 1975. Freshwater unionacean clams (Mollusca: Pelecypoda) of North America. Hamburg, Michigan: Malacological Publications.