Groundwater in the Big Lost River Basin is vital to irrigated agriculture in the basin and water users are concerned about declining groundwater levels. The U.S. Geological Survey, in cooperation with the Idaho Department of Water Resources, developed a hydrogeologic framework to provide a conceptual understanding of groundwater resources in the Big Lost River Basin. A three-dimensional hydrogeologic framework model of the Big Lost River Basin was generated to represent the subsurface distribution and thickness of four hydrogeologic units. The primary source of data for the hydrogeologic framework model was lithologic data from a well database (621 wells) compiled for this purpose. The well database was built from well-driller reports (584 wells) in Idaho Department of Water Resources files, groundwater level monitoring wells (20) in U.S. Geological Survey and Idaho Department of Water Resources files, and synthetic wells (17) defined in this study. This dataset represents the well database, distributed as three comma-delineated CSV files containing the following well information: well location, lithology, and well construction. This well database and the accompanying hydrogeologic framework model file comprise the complete hydrogeologic framework data release.