This data release is the update of the U.S. Geological Survey (USGS) - ScienceBase data release Bera (2022b), with the processed data for the period October 1, 2020, through September 30, 2021. This data release describes the watershed data management (WDM) database file WBDR21.WDM. The WDM database file WBDR20.WDM (Bera, 2022b) is updated with the quality-assured and quality-controlled meteorological and hydrologic data for the period October 1, 2020, through September 30, 2021, following the guidelines documented in Bera (2017) and is renamed as WBDR21.WDM. Meteorological data other than precipitation (wind speed, solar radiation, air temperature, dew point temperature, and potential evapotranspiration) are copied from ARGN21.WDM and stored in this WDM file. Bera (2022a) describes the processing of the meteorological data in the database file ARGN21.WDM. Data in dataset number (DSN) 107 and 801–811 are used in comparisons of precipitation data. DSN 107 contains hourly precipitation data from tipping bucket rain gages collected at Argonne National Laboratory at Argonne, Illinois. DSN 801-811 contains the processed Next Generation Weather Radar (NEXRAD)-Multisensor Precipitation Estimates (MPE) data from 11 NEXRAD–MPE subbasins in the West Branch DuPage River watershed as described in Bera and Ortel (2018). The data are downloaded and uploaded daily into a WDM database that is used for the real-time streamflow simulation system. Data from DSN 107 and 801-811 are copied from this WDM and stored in WBDR21.WDM. DSN 107 and 801-811 are updated with the data through September 30, 2021. Data in DSN 4031 (water-surface elevation from West Branch DuPage River at Fawell Dam) is updated through September 30, 2021, similarly (Bera, 2017). The missing rainfall periods are filled with the nearby raingage data as a part of the QA/QC process. Some missing period is filled with the data from a nearby raingage in Salt Creek watershed (Bera, 2014). The complete list of missing precipitation data period and the nearby stations used to fill in those missing periods during October 1, 2020, through September 30, 2021, is given in the Table 1. Table 1 is provided in comma separated values (CSV) file format. The list of snow affected days of precipitation data and the missing and estimated period of the stage and flow data in WBDR21.WDM database during the period October 1, 2020, through September 30, 2021, are given in the USGS annual Water Data Report at https://wdr.water.usgs.gov. To open the WBDR21.WDM file, the user needs to install any of the utilities described in the section "Related External Resources" on this page. References Cited: Bera, M., 2022a, Meteorological Database, Argonne National Laboratory, Illinois, January 1, 1948 - September 30, 2021: U.S. Geological Survey data release, ​https://doi.org/10.5066/P9BBP9EJ. ____ 2022b, Watershed Data Management (WDM) Database (WBDR20.WDM) for West Branch DuPage River Streamflow Simulation, DuPage County, Illinois, January 1, 2007, through September 30, 2020: U.S. Geological Survey data release, https://doi.org/10.5066/P916P5LI. Bera, M., and Ortel, T.W., 2018, Processing of next generation weather radar-multisensor precipitation estimates and quantitative precipitation forecast data for the DuPage County streamflow simulation system: U.S. Geological Survey Open-File Report 2017–1159, 16 p., https://doi.org/10.3133/ofr20171159. Bera, M., 2017, Watershed Data Management (WDM) database for West Branch DuPage River streamflow simulation, DuPage County, Illinois, January 1, 2007, through September 30, 2013: U.S. Geological Survey Open-File Report 2017–1099, 39 p., https://doi.org/10.3133/ofr20171099. Bera, M., 2014, Watershed Data Management (WDM) database for Salt Creek streamflow simulation, DuPage County, Illinois, water years 2005–11: U.S. Geological Survey Data Series 870, 18 p., http://dx.doi.org/10.3133/ds870.