Manhattan is the most densely populated borough of New York City, its economic and administrative centre, and its historical birthplace. Locally it is often referred to simply as The City.The borough is coextensive with New York County, founded on November 1, 1683, as one of the original counties of the U.S. state of New York. The borough consists mostly of Manhattan Island, bounded by the Hudson, East, and Harlem rivers; several small adjacent islands; and Marble Hill, a small neighbourhood now on the U.S. mainland, physically connected to the Bronx and separated from the rest of Manhattan by the Harlem River.