As part of the U.S. Geological Survey (USGS) Water Availability and Use Science Program study of the Mississippi Alluvial Plain (MAP), a shapefile representing seven generalized regions of the MAP extent as defined by Painter and Westerman (2018) was compiled. The generalized regions provide a framework for analysis, visualization, and regional comparisons of local data within the MAP. Regions north of the Red River were based on those described by Ackerman (1996). The Grand Prairie region includes the area north and east of the Arkansas River and south and west of the White River within the MAP. The Cache region includes the area north and east of the White River and the area generally west of Crowley’s Ridge, which lies outside of the MAP extent (Painter and Westerman, 2018), bisects the northern part of the MAP, and has elevations 100 to 250 feet (ft) higher than the MAP (Ackerman, 1996). The Delta region, which is roughly equivalent to the Yazoo River drainage, lies predominately in Mississippi and covers much of the area east of the Mississippi River within the MAP. The Boeuf region covers the area north of the Red River and the Little Old River - Mississippi River confluence, the area south of the Arkansas River, and the area west of the Delta region within the MAP. The St. Francis region lies generally east of Crowley’s Ridge and north of the Delta region in parts of Tennessee, Kentucky, Illinois, Missouri, and Arkansas. The regions south of the Red River and the Little Old River – Mississippi River confluence were based primarily on depositional environment (Saucier, 1994). The Atchafalaya region contains the Atchafalaya River. The Deltaic and Chenier Plains region lies south of the Atchafalaya region and covers the southernmost part of the MAP. In order to keep the regions contiguous, some relatively small parts of the Deltaic and Chenier Plains as defined by Saucier (1994) were included within the boundary of the Atchafalaya region defined for this study, and vice-versa. References Ackerman, D.J., 1996, Hydrology of the Mississippi River Valley alluvial aquifer, South-Central United States: U.S. Geological Survey Professional Paper 1416-D, 56 p., 8 pls. in pocket. Painter, J.A., and Westerman, D.A., 2018, Mississippi Alluvial Plain extent, November 2017: U.S. Geological Survey data release, https://doi.org/10.5066/F70R9NMJ. Saucier, R.T., 1994, Geomorphology and Quaternary geologic history of the Lower Mississippi Valley: U.S. Army Engineer Waterways Experiment Station, Vicksburg, MS, Vols. I and II, 398 p., 28 pls.