This data release provides a monthly irrigation water use reanalysis for the period 2000-20 for all USGS Watershed Boundary Dataset of Subwatersheds (Hydrologic Unit Code 12 [HUC12]) in the conterminous United States (CONUS). Results include reference evapotranspiration (ETo), actual evapotranspiration (ETa), irrigated areas, consumptive use, and effective precipitation for each HUC12. ETo and ETa were estimated using the operational Simplified Surface Energy Balance (SSEBop, Senay and others, 2013; Senay and others, 2020) model executed in the OpenET (Melton and others, 2021) web-based application implemented in Google Earth Engine. Results provided by OpenET/SSEBop were summarized to hydrologic response units (HRUs) in the National Hydrologic Model (NHM; Regan and others, 2019) to estimate consumptive use and effective precipitation on irrigated lands. Irrigated lands for the CONUS were provided by the Landsat-based Irrigation Dataset (LANID; Xie and others, 2019) for each year of the reanalysis period. Consumptive use estimates provided by the NHM were disaggregated to HUC12s using area weighted intersections with HRUs and the relative proportion of irrigated lands in each intersected area. This data release includes data and source code required to develop the irrigation reanalysis workflow along with the scripts and data required to replicate the output results. The workflow has three main steps that were automated using python scripts: 1) convert daily OpenET/SSEBop results into input for the NHM, 2) run a modified version of the NHM that is an application of the GSFLOW software package (GSFLOW version 2.3) to estimate daily results, and 3) post-process NHM results to monthly, then summarize and disaggregate ETo, ETa, irrigated areas, consumptive use, and effective precipitation to all HUC12s in the CONUS for the period 2000-20.