A two-dimensional, steady-state groundwater analytic-element flow model, GFLOW (version 2.2.3), was developed to provide a better understanding of the groundwater-surface water interactions of Crystal Lake, in the city of Crystal Lake, Illinois, in response to lowering an outlet weir during current, wet, and dry conditions. Three models were created and calibrated for average 2020 (current) conditions, wet (2017) conditions, and dry (2012) conditions with the current weir elevation and current steady-state stage-flows at the outlet weir. Simulations of groundwater and surface water responses surrounding the lake and lake-water budgets were run to understand the effects and influences of lowering the weir elevation by 1 foot, and then by lowering the weir elevation and increasing the steady-state stage-flows at the outlet weir. This U.S. Geological Survey (USGS) data release contains all of the input and output files for the simulations described in the associated model documentation report (https://doi.org/10.3133/sir20245007).