This model archive contains the model files for the MERAS 3 and Mississippi Delta groundwater flow models documented in the U.S. Geological Survey Scientific Investigations Report 2023-5100. The MERAS 3 model provides a simplified representation of groundwater flow in the Mississippi Embayment Regional Aquifer Study (MERAS) area for the period of 1900 through 2018, with the primary goal of providing boundary fluxes for inset models focused on local areas of interest. The Mississippi Delta model simulates groundwater flow in the Delta region of northwestern Mississippi from 1900 through 2018, using boundary fluxes from the MERAS 3 model. A scenario version of the Mississippi Delta model extends the simulation to 2056, using net infiltration, surface water runoff, and irrigation pumping derived from downscaled general circulation model output, via a soil water balance simulation. Workflows for initial model construction, parameter estimation, and the setup of future climate scenarios are included in separate ZIP archives, along with portable python distributions for running the workflow scripts on OSX or Windows platforms. See the Readme.md file(s) for instructions.