Resident Population in Nassau County, NY was 1392.43800 Thous. of Persons in January of 2024, according to the United States Federal Reserve. Historically, Resident Population in Nassau County, NY reached a record high of 1428.83800 in January of 1970 and a record low of 1286.90500 in January of 1990. Trading Economics provides the current actual value, an historical data chart and related indicators for Resident Population in Nassau County, NY - last updated from the United States Federal Reserve on September of 2025.