The U.S. Geological Survey (USGS), in cooperation with the Massachusetts Department of Conservation and Recreation, Office of Water Resources, developed regional regression equations for estimating selected low-flow statistics in Massachusetts. This data release contains the datasets used in the regression analyses for the regional low-flow equations for the mainland area of Massachusetts, which excludes the Plymouth-Carver-Kingston-Duxbury aquifer system area of southeastern Massachusetts and Cape Cod. Selected at-site streamflow statistics are provided for the 99-, 98-, 95-, 90-, 85-, 80-, 75-, 70-, 60-, 50-, 40-, 30-, 25-, 20-, 15-, 10-, 5-, 2-, and 1-percent flow durations; monthly 90- and 50-percent flow durations; monthly median of the monthly means; harmonic mean; median of the annual 7-day low-flow; and 7-day, 2-year (7Q2), 7-day, 10-year (7Q10), 30-day, 2-year (30Q2), and 30-day, 10-year low-flow frequencies for 174 USGS streamgages in and near Massachusetts. These streamflow statistics were computed using daily mean streamflow data through water year 2022 for non-frequency statistics and through climate year 2021 for the low-flow frequency statistics. Basin characteristics (hydrography, elevation, physical, land use, soil, surficial geology, and climate) are also provided for 174 streamgages. A geographic information system (GIS) coverage of the streamflow variability index (SVI) was developed as a basin characteristic for southern New England and eastern New York and used in the regional regression analyses. GIS coverages are provided for the regression equation explanatory variables: SVI, SSURGO hydrologic soils type A and B, and Parameter-elevation Regressions on Independent Slopes Model (PRISM) mean annual temperature 1981-2010. The Weighted-Multiple-Linear Regression (WREG) input and output files used to develop the final regional regression equations for Massachusetts are also provided.