The Cincinnati Zoo & Botanical Garden is the sixth oldest zoo in the United States, founded in 1873 and officially opening in 1875. It is located in the Avondale neighborhood of Cincinnati, Ohio. It originally began with 64.5 acres (26.1 ha) in the middle of the city, but has spread into the neighboring blocks and several reserves in Cincinnati's outer suburbs. It was appointed as a National Historic Landmark in 1987.