Union Square Park's name derives from the location. This is the intersection of two major roads in New York City, Bloomingdale Road (now Broadway) and Bowery Road (now Fourth Avenue). In 1807, the former potter’s field at this location was designated as Union Place.
The summer of 1839, Union Square opened to the public. The design was inspired by residential squares of London. The design emphasized the park’s oval shape and focused on a large central fountain, which was installed for the opening of the Croton Aqueduct in 1842. As New York City’s downtown expanded northward, Union Square became an important commercial and residential center.
In 1872, the park was redesigned, including an area for the public to hold mass meetings.
The first Labor Day Celebration was held at Union Square Park on September 5, 1882. In 1928-29 Union Square was demolished to accommodate the subway. 1920s and 1930s included building the pavilion, and the Independence (Charles F. Murphy Memorial) Flagstaff (1926, sculpted by Anthony de Francisci). Other sculptures include: George Washington (1856, Henry Kirke Brown), Abraham Lincoln (1868, also Brown), Marquis de Lafayette (1873, by Frédéric-Auguste Bartholdi), and the James Fountain (1881, by Karl Adolph Donndorf).
Union Square Greenmarket with its vast section of fresh foods and flowers has been serving the public since 1976.
1985 renovations included creating a new plaza, and adding two subway kiosks. In 1986 a monument erected of Mohandas Gandhi (1986, by Kantilal B. Patel).
Two new playgrounds were constructed in 1993-94, and a restaurant opened in the sunken courtyard outside the pavilion in 1994.
In 1997 the United States Department of the Interior designated Union Square Park as a National Historic Landmark because of its significance in American labor history.