Long Island is a densely-populated island in the southeastern geographical area of the U.S. state of New York; it is also part of the New York metropolitan area. With over 8 million people, Long Island is the most populous island in the United States and the 18th-most populous in the world. The island begins at New York Harbor approximately 0.35 miles east of Roosevelt Island and extends eastward approximately 118 miles into the Atlantic Ocean and 23 miles wide at its most distant points. The island comprises four counties; Kings and Queens counties and Nassau County share the western third of the island, while Suffolk County occupies the eastern two thirds of the island. More than half of New York City's residents lived on Long Island as of 2020, in Brooklyn and in Queens. Culturally, many people in the New York metropolitan area colloquially use the term "Long Island" to refer exclusively to Nassau and Suffolk counties, and conversely, employ the term "the City" to mean Manhattan alone. The Nassau-and-Suffolk-only definition of Long Island is recognized as a "region" by the state of New York. Although geographically an island, the Supreme Court of the United States has held that given the island's extensive ties to the mainland, it should be treated like a peninsula, allowing the state to have jurisdiction within its maritime boundaries.
Long Island may refer both to the main island and the surrounding outer barrier islands. To its west, Long Island is separated from Manhattan and the Bronx by the East River tidal estuary. North of the island is Long Island Sound, across which lie Westchester County, New York, and the state of Connecticut. Across the Block Island Sound to the northeast is the state of Rhode Island. Block Island—which is part of Rhode Island—and numerous smaller islands extend further into the Atlantic. To the extreme southwest, Long Island, at Brooklyn, is separated from Staten Island and the state of New Jersey by Upper New York Bay, the Narrows, and Lower New York Bay.
The longest and the largest island in the contiguous United States, Long Island extends 118 miles (190 km) eastward from New York Harbor to Montauk Point, with a maximum north-to-south distance of 23 miles (37 km) between Long Island Sound and the Atlantic coast. With a land area of 1,401 square miles (3,630 km2), Long Island is the 11th-largest island in the United States and the 149th-largest island in the world—larger than the 1,214 square miles (3,140 km2) of the smallest U.S. state, Rhode Island.
With an enumerated population of 8,063,232 residents as of the 2020 U.S. Census, constituting 40% of the State of New York's population, Long Island is the most populated island in any U.S. state or territory, the third-most populous island in the Americas (after only Hispaniola and Cuba), and the 18th-most populous island in the world (ahead of Ireland, Jamaica, and Hokkaidō). Its population density is 5,859.5 inhabitants per square mile (2,262.4/km2). If Long Island geographically constituted an independent metropolitan statistical area, it would rank fourth most populous in the United States; while if it were a U.S. state, Long Island would rank thirteenth in population and first in population density. Long Island is culturally and ethnically diverse, featuring some of the wealthiest and most expensive neighborhoods in the world near the shorelines, as well as working-class areas in all four counties.
As of 2019, Long Island had a gross domestic product of $197 billion. Between 2014 and 2019, Long Island experienced 4.3% growth in jobs. Median income on the island is $112,000 and the median home price is $450,000. Among those over the age of 25, 42.6% hold a college degree or higher educationally.
As a hub of commercial aviation, Long Island is home to two of the nation's and New York City metropolitan area's three busiest airports, JFK International Airport and LaGuardia Airport, in addition to Long Island MacArthur Airport; as well as two major air traffic control radar facilities, the New York TRACON and the New York ARTCC. Nine bridges and thirteen navigable tunnels (road and railroad tunnels but not metropolitan water tunnels) connect Brooklyn and Queens to the three other boroughs of New York City. Ferries connect Suffolk County northward across Long Island Sound to the state of Connecticut. The Long Island Rail Road is the busiest commuter railroad in North America and operates continually. Nassau County high school students often feature prominently as winners of the International Science and Engineering Fair and similar STEM-based academic awards. Biotechnology companies and scientific research play a significant role in Long Island's economy, including research facilities at Brookhaven National Laboratory, Cold Spring Harbor Laboratory, Stony Brook University, New York Institute of Technology, Plum Island Animal Disease Center, the New York University Tandon School of Engineering, the Hofstra Northwell School of Medicine, and the Feinstein Institutes for Medical Research.