We present detrital-zircon U–Pb geochronology from the Mississippi, Mobile, and Apalachicola rivers, as well as five beach and barrier island deposits to determine sediment sources, alongshore transport, and sediment mixing in the northeastern Gulf of Mexico. The Mississippi River has a distinct age spectrum defined by prominent Cenozoic and Mesozoic populations coupled with minor Appalachian (490-270 Ma), Grenville (1200-900 Ma), Granite-Rhyolite (1500-1300 Ma), and Yavapai-Mazatzal (1800-1600 Ma) populations. The Mobile and Apalachicola rivers exhibit age spectra containing few to no Cenozoic grains, are proportionately dominated by Appalachian and Grenville populations, and have minor populations consisting of Iaptian Rifting/Gondwanan (850-550 Ma), Granite-Rhyolite, and Yavapai-Mazatzal ages. Comparison of U–Pb age spectra and inverse mixing models shows that beach and barrier island deposits are primarily derived of material from the Apalachicola River, with Mobile River contribution being dependent on geographic position west of Mobile Bay. Minor Mississippi River contribution in coastal deposits results from shelf bypass to deep marine sinks and when present is likely associated with recycling of Coastal Plain strata. Metamorphic zircon grain abundance (14–36%) in coastal deposits and chemical-age relationships to southern Appalachian eastern Blue Ridge and Inner Piedmont provinces corroborate Apalachicola and or Mobile river system provenance. Results from this study suggest that anthropogenic influences and hurricanes have little to no effect on the detrital-zircon age spectra at a regional scale, and that the northeastern Gulf of Mexico can be used as an analog for older Cenozoic and Mesozoic source to sink investigations in the eastern Gulf Coastal Plain.