Bronx River in the context of "Thain Family Forest"

The Bronx (/brɒŋks/ BRONKS) is the northernmost of the five boroughs of New York City, coextensive with Bronx County, in the U.S. state of New York. The borough shares a land border with Westchester County, New York to its north; to its south and west, the New York City borough of Manhattan lies across the Harlem River; and to its south and east is the borough of Queens, across the East River. The Bronx, the only New York City borough located primarily on the U.S. mainland, has a land area of 42 square miles (109 km) and a population of 1,472,654 at the 2020 census. It has the fourth-largest area, fourth-highest population, and third-highest population density of the boroughs.

The Bronx is divided by the Bronx River into a hillier section in the west, and a flatter eastern section. East and west street names are divided by Jerome Avenue. The West Bronx was annexed to New York City in 1874, and the areas east of the Bronx River in 1895. Bronx County was separated from New York County (modern-day Manhattan) in 1914. About a quarter of the Bronx's area is open space, including Woodlawn Cemetery, Van Cortlandt Park, Pelham Bay Park, the New York Botanical Garden, and the Bronx Zoo in the borough's north and center. The Thain Family Forest at the New York Botanical Garden is thousands of years old and is New York City's largest remaining tract of the original forest that once covered the city. These open spaces are primarily on land reserved in the late 19th century as urban development progressed north and east from Manhattan. The Bronx is also home to Yankee Stadium of Major League Baseball.

The City of Greater New York was the consolidation of the City of New Yorkwith Brooklyn, western Queens County, and Staten Island, which took effect on January 1, 1898. New York had already annexed the Bronx (west of the Bronx River in 1874, east of the Bronx River in 1895), so the consolidated city sprawled across five counties, which became the five Boroughs of modern New York. Eastern Queens County was excluded and later became Nassau County.

The West Bronx is a region in the New York City borough of the Bronx. The region lies west of the Bronx River and roughly corresponds to the western half of the borough.

The West Bronx is more densely populated than the East Bronx, and is closer to Upper Manhattan. From the late 17th century to the middle 19th century this included the central and southern part of the Town of Yonkers, but then became the separate Town of Kingsbridge. In 1874, the then towns of Kingsbridge, West Farms and Morrisania were transferred to New York County, becoming the first area outside Manhattan to be annexed by the City of New York. Today's West Bronx was then known as the "Annexed District". In 1895, the city annexed the modern-day East Bronx, followed in 1898 by western Queens County (today's borough of Queens, with the remainder of what was eastern Queens County becoming the newly formed Nassau County), all of the City of Brooklyn (today's borough of Brooklyn), and all of Richmond County (today's borough of Staten Island) to form the consolidated city of New York.

The East Bronx is the part of the New York City borough of the Bronx which lies east of the Bronx River; this roughly corresponds to the eastern half of the borough. Neighborhoods include: Baychester, Castle Hill, City Island, Co-op City, Country Club, Eastchester, Edenwald, Edgewater Park, Harding Park, Morris Park, Parkchester, Pelham Bay, Pelham Parkway, Soundview, Throggs Neck, Van Nest, Wakefield, Westchester Square, and Williamsbridge.

The East Bronx is less densely populated than the West Bronx. While the West Bronx is older and its underlying Fordham gneiss is very hilly, the East Bronx is not only later-settled but also underlain by younger schist and in most parts flat and coastal, much like the neighboring borough of Queens. The East Bronx was annexed by the City of New York decades later; the West Bronx in 1874, while the East Bronx remained part of Westchester County until 1895.

The Bronx Zoo (also historically the Bronx Zoological Park and the Bronx Zoological Gardens) is a zoo within Bronx Park in the Bronx, New York City. It is one of the largest zoos in the United States by area and the largest metropolitan zoo, comprising 265 acres (107 ha) of park lands and naturalistic habitats separated by the Bronx River. The zoo has 2.1 million average yearly visitors as of 2009. The zoo's original buildings, known as Astor Court, were designed as a series of Beaux-Arts pavilions grouped around the large circular sea lion pool. The Rainey Memorial Gates were designed by sculptor Paul Manship in 1934 and listed on the National Register of Historic Places in 1972.

The zoo opened on November 8, 1899, featuring 843 animals in 22 exhibits. Its first director was William Temple Hornaday, who served for 30 years. From its inception the zoo has played a vital role in animal conservation. In 1905, the American Bison Society was created in an attempt to save the American bison, which had been depleted from tens-of-millions of animals to only a few hundred, from extinction. Two years later they were successfully reintroduced into the wild. In 2007, the zoo successfully reintroduced three Chinese alligators into the wild. The breeding was a milestone in the zoo's 10-year effort to reintroduce the species to the Yangtze River in China.

Bronx Park is a public park along the Bronx River, in the Bronx, New York City. The park is bounded by Southern Boulevard to the southwest, Webster Avenue to the northwest, Gun Hill Road to the north, Bronx Park East to the east, and East 180th Street to the south. With an area of 718 acres (2.91 km), Bronx Park is the eighth-largest park in New York City.

Founded in the late 1880s, Bronx Park is the location of the New York Botanical Garden and the Bronx Zoo, which respectively occupy much of the northern and southern portions of the park. Fordham Road runs east–west between the zoo and botanical garden, bisecting Bronx Park, while the Bronx River Parkway runs north–south near the eastern edge. The park is operated by the New York City Department of Parks and Recreation.