Long Island is an island located just off the northeast coast of the United States and a region within the U.S. state of New York. Stretching east-northeast from New York Harbor into the Atlantic Ocean, the island comprises four counties: Kings and Queens (these form the New York City boroughs of Brooklyn and Queens, respectively) to the west; then Nassau and Suffolk to the east. However, many people in the New York metropolitan area (even those living in Queens and Brooklyn) colloquially use the term "Long Island" (or "The Island") exclusively to refer to the Nassau-Suffolk county area collectively, which is mainly suburban in character. More generally, "Long Island" may also refer collectively to the main Island as well as its nearby, surrounding outer barrier islands. North of the island is the Long Island Sound, across from which lie the states of Connecticut and a small part of Rhode Island across the Block Island Sound. Westchester County on mainland New York lies across the Sound to the northwest. To the west, Long Island is separated from the Bronx and the island of Manhattan by the East River. To the extreme southwest, it is separated from Staten Island and New Jersey by Upper New York Bay, the Narrows, and Lower New York Bay. To the East lies Block Island and numerous smaller islands.
With a Census-estimated population of 7,838,722 in 2015, constituting nearly 40% of the state's population, Long Island is the most populated island in any U.S. state or territory, and the 18th-most populous island in the world (ahead of Ireland, Jamaica, and Hokkaidō). Its population density is 5,571 inhabitants per square mile (2,151/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 13th in population and first in population density.
Both 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 state, Rhode Island.
Two of the New York City metropolitan area's three busiest airports, JFK International Airport and LaGuardia Airport, as well as two major air traffic control radar facilities, the New York TRACON and the New York ARTCC, are located on the Island. Nine bridges and 13 tunnels (including railroad tunnels) connect Brooklyn and Queens (and thus Long Island) to the three other boroughs of New York City. Ferries connect Suffolk County northward across Long Island Sound to the state of Connecticut. In addition, the Long Island Rail Road is the busiest commuter railroad in North America and operates 24/7.