Brooklyn is the most populous of New York City's five boroughs, with about 2.6 million people as well as the second-largest in area. Since 1896, Brooklyn has had the same boundaries as Kings County, which is the most populous county in New York and the second-most densely populated county in the United States, after New York County (Manhattan). Today, if it were an independent city, Brooklyn would rank as the fourth most populous city in the U.S., behind only the other boroughs of New York combined, Los Angeles, and Chicago.

Brooklyn was an independent incorporated city (and previously an authorized village and town within the provisions of the New York State Constitution, until January 1, 1898 when, after a long political campaign and public relations battle during the 1890's, according to the new Municipal Charter of "Greater New York", Brooklyn was consolidated with the other cities, boroughs and counties to form the modern "City of New York" surrounding the Upper New York Bay with five constituent boroughs. It continues however to maintain a distinct culture, as befitting the former second or third largest city in America during the later 19th Century. Many Brooklyn neighborhoods are ethnic enclaves where particular ethnic and nationality groups and cultures predominate. Brooklyn's official motto is Eendraght Maeckt Maght. Written in the (early modern spelling of the) Dutch language, it is inspired by the motto of the United Dutch Provinces (first Dutch Republic, predecessor of the current Kingdom of the Netherlands), (currently also the official motto of the neighboring Kingdom of Belgium) and translated "In unity, there is strength." The motto is displayed on the Borough seal and flag, which also feature a young robed woman bearing a bundle of bound rods known as a "fasces", a traditional emblem of Republicanism. Brooklyn's official colors are blue and gold.

Brooklyn has a high degree of linguistic diversity. As of 2010, 54.12% (1,240,416) of Brooklyn residents age 5 and older spoke English at home as a primary language, while 17.16% (393,340) spoke Spanish, 6.46% (148,012) Chinese, 5.31% (121,607) Russian, 3.47% (79,469) Yiddish, 2.75% (63,019) French Creole, 1.35% (31,004) Italian, 1.20% (27,440) Hebrew, 1.01% (23,207) Polish, 0.99% (22,763) French, 0.95% (21,773) Arabic, 0.85% (19,388) various Indic languages, 0.70% (15,936) Urdu, and African languages were spoken as a main language by 0.54% (12,305) of the population over the age of five. In total, 45.88% (1,051,456) of Brooklyn's population age 5 and older spoke a mother language other than English.