Chicago Zoological Park, or Brookfield Zoo, a zoo in Brookfield, Illinois. It covers 215 acres (87 hectares) 14 miles (23 km) west of downtown Chicago. The zoo has one of the largest and most varied collections in the United States. There are approximately 2,500 animals, representing more than 400 species. Many are housed in barless enclosures that simulate their natural environment. Special exhibits include the Children's Zoo; Seven Seas Panorama, an indoor dolphin show; Tropic World, an indoor tropical rain forest; and Habitat Africa!, an African wildlife exhibit. The zoo opened in 1934. It is operated by the Chicago Zoological Society, a private nonprofit organization.