This data set includes estimated chloride concentrations for the 93 USGS water quality monitoring stations located across the eastern United States. Chloride concentrations were predicted using regression equations that established the relationship between simultaneous measurements of chloride and specific conductance (SC). Site-specific models were developed and applied when data were available, and regional regression models were used where there were insufficient data available to establish a site-specific regression model. These models were applied to high-frequency SC data sets to produce high-frequency predicted chloride concentrations at 2-minute to 1-hour intervals, depending on the frequency at which SC is measured at each site. Up to four chloride concentration estimations may be available for a particular site, depending on whether a simple linear regression was developed (SLR), a piecewise regression was developed (SEG), and whether or not site-specific models were developed and applied. The best-fitting regional regression model was applied to all 93 sites. Regions include the southeast, Mid-Atlantic, Mid-Atlantic carbonate (e.g., underlain with carbonate bedrock), and New England, and correspond to the regions included in Moore and others (in review). Each file is labeled by its short name. Please see "Chloride_site_information.csv" for the corresponding site IDs and the USGS station numbers. Moore, J., R. Fanelli, and A. Sekellick. In review. High-frequency data reveal deicing salts drive elevated conductivity and chloride along with pervasive and frequent exceedances of the EPA aquatic life criteria for chloride in urban streams. Submitted to Environmental Science and Technology.