This dataset provides historical and climate projection monthly hydropower generation timeseries for HUC4 watersheds within the contiguous U.S. (CONUS). These data were developed as an extension to the Department of Energy Water Power Technologies Office's SECURE Water Act Section 9505 Third Assessment (9505) and include both federal and non-federal hydropower facilities. Additional modeling detail can be found in Broman et al., 2024 and in the article's metarepository. Note that in some instances multiple HUC4 watersheds have been merged together into a HUC4 group, and that HUC4 watersheds without hydropower facilities are excluded. A hydropower facility's physical location, rather than the source of water, was used in assigning facilities to HUC4 watersheds. The dataset is provided in three separate formats to facilitate ease of use: 1) Machine-readable csv in 'tidy' data format: Short Name Unit Description class N/A simulation type; control: historical, cc: climate scenario forcing N/A meteorological forcing used to drive hydrology model model N/A hydrology model hp N/A hydropower model gcm* N/A global climate model name ds* N/A downscaling method; DBCCA (statistical), RegCM (dynamical) HUC4_group N/A HUC4 group; HUC4 numeric ID or multiple IDs year N/A year month N/A month modeled_generation_MWh MWh per month simulated generation * only present in the climate projection (cc) files 2) xlsx with HUC4 group data by tab 3) csv by HUC4 group: for historical data: year, month, and HUC4_group columns are the same as above. Data column headers are class_forcing_model_hp and with the units MWh per month. for climate projection (cc) data: year, month, and HUC4_group columns are the same as above. Data column headers are class_forcing_model_hp_gcm_ds and with the units MWh per month.