The Mississippi Sound is underlain by late Pleistocene aged sediments of the Biloxi, Prairie, and Gulfport Formations topped by an erosional unconformity, which was an exposed land surface during the sea level low-stand of the last glacial maximum. During that period, rivers and streams draining upland watersheds cut across the exposed coastal plain incising a network of distributary fluvial channels. Subsequent sea level rise covered the incised drainage network with a relatively thin (10-20 m) layer of reworked Holocene aged sediments. Here, an extensive database of archived and newly collected seismic reflection profile data, as well as archived core data, is analyzed to map the paleotopography and the paleo-drainage network of the Pleistocene-Holocene unconformity surface beneath the western Mississippi Sound. Approximately 255 km of seismic data was acquired with a 2-16 kHz chirp sub-bottom profiling sonar. Additionally, 978 km of seismic data was accessed through a United States Geological Survey archive along with over 20 historical cores. Results indicate that the Pleistocene-Holocene unconformity under the western Mississippi Sound is gently dipping to the southeast (<0.05°) and contains a complex network of incised paleofluvial channels with relief ranging from 5-10 m and widths ranging from 0.3–2 km. A conceptual model for paleo-channel incision and infilling as well as modern analogue depositional environments are presented.