This data release contains the input, output, and model code used to run a transient simulation of a previously published (Walter and others, 2020) steady-state regional model of Long Island, N.Y. The original model code was updated to MODFLOW 6 (version 6.3.0) and incorporates monthly transient stress periods to simulate conditions from 2005-2019 following methods described in Walter and others (2020). Selected remedial stresses (groundwater extraction and return) were incorporated for select locations in southeastern Nassau County. No modifications were made to the hydrologic boundaries, model layers, or hydraulic properties specified in the original model. A uniform value of 0.25 was used to represent specific yield (unconfined storage) and a uniform value of 0.00001 was used to represent specific storage (confined storage) which are typical values for Long Island sediments. Monthly values for natural recharge from precipitation were calculated using a Soil-Water Balance model (Finkelstein and others, 2022). Components of anthropogenic recharge--wastewater return flow, storm water inflow, and inflow from leaky infrastructure--were estimated for monthly stress periods consistent with the methods described in Walter and others (2020). Monthly groundwater withdrawals for various sources, including public-water supply, industrial, remediation, and agricultural, were compiled or estimated for the same period. No additional calibration was conducted for this scenario and as such, it is possible that in some locations the model simulation results may not accurately represent the temporal responses to monthly hydrologic stresses.