Queens is the easternmost and largest in area of the five boroughs of New York City. It is geographically adjacent to the borough of Brooklyn at the southwestern end of Long Island, and to Nassau County further east on Long Island; in addition, Queens shares water borders with the boroughs of Manhattan and the Bronx. The borough of Queens is the second-largest in population (after Brooklyn), with a census-estimated 2,339,150 residents in 2015. Queens County is also the second-most populous county in New York, behind the neighboring borough of Brooklyn. Queens is the fourth-most densely populated county among New York City's boroughs, as well as in the United States. If each of New York City's boroughs were an independent city, Queens also would be the nation's fourth most populous city, after Los Angeles, Chicago, and Brooklyn.

Queens was established in 1683 as one of the original 12 counties of New York. It was named after the Portuguese Princess Catherine of Braganza (1638–1705), Queen of England, Scotland, and Ireland. It became a borough of New York City in 1898.

Brooklyn is the most populous of New York City's five boroughs, with a Census-estimated 2,636,735 residents in 2015.It borders the borough of Queens at the southwestern end of Long Island. Since 1896, Brooklyn has had the same boundaries as Kings County, the most populous county in New York, and the second-most densely populated county in the United States, after the county of New York (the borough of Manhattan).

With a land area of 71 square miles and water area of 26 square miles, Kings County is New York's fourth-smallest county by land area and third-smallest by total area, though it is the second-largest among the city's five boroughs. Today, if each of the five boroughs were a separate city, Brooklyn would rank as the third-most populous city in the U.S., behind Los Angeles and Chicago.