This report presents miscellaneous geologic, hydrologic, and ground-water-quality data collected in and near Belvidere, Ill. during May 2001–November 2002. The data were collected for two studies conducted by the U.S. Geological Survey during 1990–2002, but subsequent to publication of the final interpretive reports for the studies. The cooperative studies with the U.S. Environmental Protection Agency and Illinois Environmental Protection Agency evaluated the hydrogeology, ground-water-flow system, and distribution of contaminants in the glacial drift and bedrock (primarily Galena-Platteville) aquifers underlying the vicinity of Belvidere, including the Parson's Casket Hardware Superfund site. Data presented in the report include lithologic descriptions, geophysical logs, water levels, hydraulic characteristics, field-measured characteristics of water quality, and laboratory analyses of volatile organic compounds, major ions, trace elements, nutrients, and herbicides.