Brooklyn is a borough of New York City, coextensive with Kings County, in the U.S. state of New York. Kings County is the most populous county in the State of New York, and the second-most densely populated county in the United States, following New York County, which is co-extensive with the neighboring New York City borough of Manhattan.[a] Brooklyn is also New York City's most populous borough, with 2,736,074 residents in 2020. If each borough were ranked as a city, Brooklyn would rank as the third-most populous in the U.S., after Los Angeles and Chicago.

Since its consolidation with New York City in 1898, Brooklyn has been governed by the New York City Charter that provides for a "strong" mayor–council system. The centralized government of New York City is responsible for public education, correctional institutions, public safety, recreational facilities, sanitation, water supply, and welfare services. On the other hand, the Brooklyn Public Library is an independent nonprofit organization partially funded by the government of New York City, but also by the government of New York State, the U.S. federal government, and private donors.

Democrats hold most public offices, and the borough leans heavily Democratic. As of November 2017, 89.1% of registered voters in Brooklyn were Democrats. Party platforms center on affordable housing, education and economic development. Pockets of Republican influence exist in Gravesend, Bensonhurst, Bay Ridge, Dyker Heights and Midwood.