Nassau County, New York

Nassau County ( ) is a densely populated and affluentsuburbancounty located on Long Island, immediately to the east of New York City, bordering the Long Island Sound on the north and the open Atlantic Ocean to the south. As of the 2020 United States census, Nassau County's population was 1,395,774, making it the sixth-most populous county in the State of New York and 29th in the nation, reflecting an increase of 56,242 (+4.2%) from the 1,339,532 residents enumerated at the 2010 census. By 2025, Nassau's population was approaching 1.4 million, driven by a high influx of Asians. The county seat is Mineola, while Nassau County's largest and most populous town is Hempstead.

Situated on western Long Island, the County of Nassau borders New York City's borough of Queens to its west, and Long Island's Suffolk County to its east. It is the most densely populated and second-most populous county in the State of New York outside of New York City, with which it maintains extensive rail, highway, and cultural connectivity. Nassau is considered one of the central counties within the New York metropolitan area.

The county comprises two cities, three towns, 64 incorporated villages, and more than 60 unincorporated hamlets. Nassau County has a designated police department, fire commission, and elected executive and legislative bodies.

A 2012 Forbes article based on the American Community Survey reported Nassau County as the most expensive county and one of the highest-income counties in the U.S., and the most affluent in New York state, with four of the nation's top ten towns by median household income located in the county. As of 2025, the median home price overall in Nassau County is nearly US$900,000, while the Gold Coast of Nassau County features some of the world's most expensive real estate. Nassau has also been ranked as one of the safest counties in the United States.

Nassau County high school students often feature prominently as winners of the International Science and Engineering Fair and similar STEM-based academic awards as well as top U.S. schools lists. Cold Spring Harbor Laboratory in the Town of Oyster Bay; the Old Westbury campus of New York Institute of Technology; the second campus of the New York University Grossman School of Medicine in Mineola, Zucker School of Medicine in the Village of Hempstead; and the Feinstein Institutes for Medical Research in Manhasset, are prominent life sciencesresearch and academic institutions in Nassau County. The presence of numerous prominent health care systems has made Nassau County a central hub for advanced medical care and technology. Eight cricket matches of the 2024 ICC Men's T20 World Cup were played at a temporary cricket stadium in Eisenhower Park in East Meadow in June 2024.