A previously developed three-dimensional steady-state groundwater flow model (https://doi.org/10.3133/sir20205091) is used to assist resource managers and planners in developing informed strategies to address nitrogen loading to coastal water bodies of Long Island, New York. Coastal water bodies of Long Island are important economic and recreational resources for the region. Therefore, the U.S. Geological Survey and New York State Department of Environmental Conservation initiated a program to delineate a comprehensive dataset of CAs (or areas contributing groundwater), travel times, and groundwater discharges to streams, lakes, marine-surface waters, and subsea discharge boundaries. The 25-layer regional groundwater-flow model of average regional hydrologic conditions used MODFLOW-NWT and MODPATH6 (for the particle-tracking analysis) to delineate CAs to 843 water bodies. Two steady-state conditions were simulated: pre-pumping conditions and recent conditions from 2005 to 2015. One hundred particles evenly distributed across the top of each 500- by 500-foot model cell that receives recharge at the water table, were tracked forward to discharge zones. This USGS data release contains all of the input and output files for the simulations described in the associated model documentation report (https://doi.org/10.3133/sir20215047).