The U.S. Geological Survey (USGS), in cooperation with DuPage County Department of Engineering, Stormwater Management Division, maintains a database of hourly meteorologic and hydrologic data for use in a near real-time streamflow simulation system, which assists in the management and operation of reservoirs and other flood-control structures in the Salt Creek watershed in DuPage County, Illinois. The majority of the precipitation data are collected from a tipping-bucket rain-gage network located in and near DuPage County. The other meteorologic data (wind speed, solar radiation, air temperature, and dewpoint temperature) are collected at Argonne National Laboratory in Argonne, Illinois. Potential evapotranspiration is computed from the meteorologic data. The hydrologic data (discharge and stage) are collected at USGS streamflow-gaging stations in DuPage County. These data are stored in a Watershed Data Management (WDM) database. This report describes a version of the WDM database that was quality-assured and quality-controlled annually to ensure the datasets were complete and accurate. This version of the WDM database contains data from January 1, 1997, through September 30, 2004, and is named SEP04.WDM. This report provides a record of time periods of poor data for each precipitation dataset and describes methods used to estimate the data for the periods when data were missing, flawed, or snowfall-affected. The precipitation dataset data-filling process was changed in 2001, and both processes are described. The other meteorologic and hydrologic datasets in the database are fully described in the annual U.S. Geological Survey Water Data Report for Illinois and, therefore, are described in less detail than the precipitation datasets in this report.