The Mississippi Alluvial Plain (MAP) Project contains several geologic units which act as important aquifers. We collected several sets of time-domain electromagnetic (TEM) data consisting of two higher-density surveys and six regional-scale transects. The higher density surveys were collected to compare and contrast to other geophysical data not included in this data release, such as airborne electromagnetic, magnetic resonance sounding, and towed time-domain electromagnetic surveys . The transects, which were collected over the span of three years, cross the MAP study area from east-to-west, with about 100 km line spacing, and cover an area of nearly 100,000 square-kilometer. Each transect spans a distance of 100-200 km, with 10-20 TEM soundings that capture the major geologic units. TEM is capable of measuring the electrical resistivity structure of the subsurface and distinguishing between geologic units that possess different electrical properties. These TEM data are being used to refine the 3D Mississippi Embayment Aquifer System Regional Groundwater Availability Study (https://www2.usgs.gov/water/lowermississippigulf/lmgweb/meras/index.html).