The Milwaukee County Zoo is a zoo in Milwaukee, Wisconsin, operated by the Milwaukee County Parks Commission and is accredited by the Association of Zoos and Aquariums. The zoo averages about 1.3 million visitors a year. The zoo houses 3,100 animals from 350 species and covers an area of 190 acres (77 ha). The zoo is noted for the second birth of polar bears and siamangs in captivity and for their locally famous gorilla Samson, who lived from 1950 to 1981 and whose bones are now on display at the Milwaukee Public Museum. During World War II, a celebrity animal of the zoo was Gertie the Duck and her ducklings. The zoo is also home to one of the largest group of bonobos in one location outside their native Democratic Republic of the Congo, and has two cheetahs from the National Zoo in Washington, DC.

The National Zoological Park, commonly known as the National Zoo, is one of the oldest zoos in the United States. The zoo is part of the Smithsonian Institution and does not charge admission. Founded in 1889, its mission is to "provide engaging experiences with animals and create and share knowledge to save wildlife and habitats".