The Forest Preserve District of Cook County is a governmental commission in Cook County, Illinois, that owns and manages a network of open spaces, containing forest, prairie, wetland, streams, and lakes, that are mostly set aside as natural areas. Cook County contains Chicago, and is the center of the most densely populated urban metropolitan area in the Midwest. The Forest Preserve lands encompass approximately , about 11% of the county, providing open space within its urban surroundings. It contains facilities for recreation, as well as a zoo and a botanic garden. Background Most often being left more in their natural state, the Forest Preserves have a different purpose from urban parks; also they generally do not contain organized recreational facilities such as tennis courts or softball diamonds. They do contain hiking, bicycling, and riding trails, as well as facilities for nature and group activities, and they are heavily used for picnicking. They are administered by the Forest Preserve District of Cook County, a special taxation district that crosses municipal boundaries. The districts headquarters is located in River Forest near Harlem Avenue and Lake Street. While the Forest Preserve District as a unit of government and municipal corporation is legally separate from Cook County, the latter's board of commissioners, the county board's president, commissioners and clerk hold the same offices ex officio concurrently, making up the Forest Preserve District Board of Commissioners. In 1905, at the instigation of the Cook County Board of Commissioners and private nature groups partly guided by prominent landscape architect Jens Jensen, Illinois adopted a forest preserve act. However, defects in the law caused it to be declared inoperable. The Forest Preserve District Association was formed in 1911 and a new state law was adopted; however, the courts declared the 1911 law unconstitutional. Finally in 1913, the State adopted a Forest Preserve Act that survived legal challenge. The 1913 law allowed a county board: A Cook County referendum required by the 1913 law was passed by voters in 1914, establishing the Forest Preserve District of Cook County, and the first Board meeting was held in February 1915. Operations In addition to owning and managing tens of thousands of acres of forest, meadow, and wetlands, both the Brookfield Zoo (managed by agreement with the Chicago Zoological Society) and the Chicago Botanic Gardens (managed by the Chicago Horticultural Society) are located on district land. The Forest Preserve District also