Periodic water-quality data were collected at four landfills in Hillsborough County from January 1974 through October 1977. Water samples were analyzed for nitrogen and phosphorous species, cations, trace metals, chloride, specific conductance, chemical oxygen demand, biological oxygen demand, and coliforms. Select ground-water samples were analyzed for herbicide and pesticide. Results of chemical and bacteriological analysis form four landfills are presented as basic data. Geologic logs and well descriptions are presented for wells drilled at the landfills after January 1974.