Maps of the distributions of the four major clay minerals (smectite, illite, kaolinite and chlorite) in and around the Mississippi River drainage basin and in the Northern Gulf of Mexico have been produced using newly acquired data from erodible/alluvial terrestrial sediments and marine surface sediments, as well as from previously published data. East of the Rockies, North America can be divided into four, large, clay-mineral provinces: (1) the northwestern Mississippi River watershed (smectite rich), (2) the Great Lakes area and eastern Mississippi River watershed (illite and chlorite rich), (3) the southeastern United States (kaolinite rich) and (4) the Brazos River and southwestern Mississippi River watersheds (illite and kaolinite rich). The clay mineral distributions in surface sediments of the present-day Gulf of Mexico are strongly influenced by three main factors: (1) by relative fluvial contributions: the Mississippi River delivers the bulk of the clay input to the Northern Gulf of Mexico whereas the Apalachicola, Mobile, Brazos and Rio Grande rivers inputs have more local influences; (2) by differential settling of various clay mineral species, which is identified for the first time in Northern Gulf of Mexico sediments; and (3) by oceanic current transport: the Gulf of Mexico surface and subsurface circulation distributes the clay-rich sediments from river mouth sources throughout the Northern Gulf of Mexico.