A monthly model of groundwater-transported nitrogen loads was developed for 12-digit hydrologic unit code (HUC12) watersheds on the north shore of Long Island Sound in coastal Connecticut and adjacent areas of New York and Rhode Island. As part of the analysis, potential management actions that upgraded septic systems or reduced fertilizer application to areas of turf-grass were also simulated. This compilation includes a zipped file (Tables.zip) of aggregated model outputs and datasets used in the model development. The zipped file contains a file dictionary (file_dictionary.csv) that includes the file name, title, and caption for each table and a data dictionary (data_dictionary.csv) that includes the variable name, data type, units, reasonable values, and a description for each column in the tables. This compilation also includes a zipped file of supplemental figures (Figure.zip) that were not included in the main report. The zipped file contains a file dictionary (file_dictionary.csv) that includes the file name, title, and caption for each figure. Finally, this compilation includes a shapefile of the HUC12 basins as used in this study. For the purposes of this study the seaward boundaries of the HUC12 basins were extended to include adjacent coastal waters and the shapefiles were delineated using the model grid. For these reasons the shapefiles will differ slightly from other geospatial datasets of the HUC12 basins. Complete model inputs and outputs are available in the model archives accessible at https://doi.org/10.5066/P1HKENGV and https://doi.org/10.5066/P1GUC7FE.