In eastern North America after ca. AD 1050, the spread of Mississippian cultures sparked widespread transformations to economy, material culture, political structure, and ideology. “Mississippianization” influenced the politically complex maritime polities of Florida’s peninsular Gulf coast, but the lack of maize agriculture indicates changes played out differently than among many inland polities. Mississippian-style pottery sherds deposited widely in mounds and in middens at the largest administrative centers are perhaps the clearest evidence of connections to the Mississippian world. We conducted a provenance study using neutron activation analysis of 303 Mississippi Period pottery vessels from 18 sites on Florida’s peninsular Gulf coast to investigate how and from where coastal communities acquired Mississippian vessel forms, paste recipes, and iconography. The sample includes numerous Mississippian-related pottery types as well as Pinellas Plain, one of the local utilitarian wares. Four chemical groups are defined, three of which are local to the peninsular Gulf coast and one that is associated with the “Deep South,” defined here as the inland Florida panhandle and Chattahoochee River area of southern Georgia. Our results indicate that most Mississippian-style vessels were locally made but used clay sources different from some utilitarian wares such as Pinellas Plain. Using distinctive clays and paste recipes, local production of Mississippian vessels may have been controlled by competing kin-based corporate groups affiliated with each mound center. The widespread low frequency of nonlocal Mississippian sherds from the Deep South shows persistent connections to inland Fort Walton and Rood Phase polities, possibly in relation to training of coastal potters. A greater prevalence of pottery from the Deep South at Shell Creek (8LL8) at the southern edge of the sampling region may reflect a polity with greater success in acquiring prestige goods, perhaps associated with the strong and expansive political power of the Calusa.