A three-dimensional, finite-difference MODFLOW 2005 groundwater model using the Newton formulation solver (MODFLOW-NWT) was created for the Cimarron River alluvial aquifer in Payne County, north-central Oklahoma to assess the impacts of current groundwater withdrawal rates with respect to current and future groundwater availability and the impacts to baseflow to the Cimarron River. To better understand current (2021) water resources and possible future water availability in the Pawnee Nation Tribal jurisdictional area, the U.S. Geological Survey, in cooperation with the Bureau of Indian Affairs and the Pawnee Nation of Oklahoma, compiled available hydrogeologic data and developed conceptual and numerical groundwater-flow models. The numerical model consists of a single layer representing alluvium and terrace deposits within the alluvial aquifer model area. The calibrated model contains one steady-state stress period and 24 monthly, transient stress periods for 2016-17. Streamflow-capture analysis was applied to the steady-state simulation to identify areas of the aquifer where base flows in the Cimarron River were most sensitive to groundwater withdrawals. This 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/sir20215073).