|Location||3400 Vine St, Cincinnati, Ohio, U.S.|
|Land area||75 acres (30 ha)|
|No. of animals||1,896|
|No. of species||500+|
|Annual visitors||1.2 million+|
The Cincinnati Zoo and Botanical Garden is the second-oldest zoo in the United States, opening in 1875, just 14 months after the Philadelphia Zoo opened on July 1, 1874. It is located in the Avondale neighborhood of Cincinnati, Ohio. It originally began with 64.5 acres (26.5 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. 
The zoo houses over 500 animals and 3,000 plant species. In addition, the zoo also has conducted several breeding programs in its history, and was the first to successfully breed California sea lions. In 1986, the Lindner Center for Conservation and Research of Endangered Wildlife (CREW) was created to further the zoo's goal of conservation. The zoo is known for being the home of Martha, the last living passenger pigeon, and to Incas, the last living Carolina parakeet.
In 1872, three years before the zoo's creation, Andrew Erkenbrecher and several other residents created the Society for the Acclimatization of Birds in Cincinnati to acquire insect-eating birds to control a severe outbreak of caterpillars. A collection of approximately 1,000 birds imported from Europe in 1872 was housed in Burnet Woods before being released. In 1873, members of the Society of Acclimatization began discussing the idea of starting a zoo and founded The Zoological Society of Cincinnati. One year later, the Zoological Society of Cincinnati purchased a 99-year lease on sixty-five acres in the cow pasture known as Blakely Woods.
The Cincinnati Zoological Gardens officially opened its doors on September 18, 1875. Architect James W. McLaughlin, who constructed the zoo's first buildings, designed the earliest completed zoological exhibits in the United States. The zoo began with eight monkeys, two grizzly bears, three white-tailed deer, six raccoons, two elk, a buffalo, a laughing hyena, a tiger, an American alligator, a circus elephant, and over four hundred birds, including a talking crow.  The first guide book about the Cincinnati Zoo was written in 1876 in German. The founders of the zoo, including its first general manager, were German immigrants and the city had quite a large German-speaking population. The first English-language edition (illustrated) was published in 1893.
In its first 20 years, the zoo experienced many financial difficulties, and despite selling 22 acres (8.9 ha) to pay off debt in 1886, it went into receivership in 1898. In order to prevent the zoo from being liquidated, the stockholders chose to give up their interests of the $225,000 they originally invested. For the next two years, the zoo was run under the Cincinnati Zoological Company as a business. In 1901, the Cincinnati Traction Company, purchased the zoo, hoping to use it as a way to market itself to potential customers. They operated the zoo until 1917, when the Cincinnati Zoological Park Association, funded by donations from philanthropists Mary Emery and Anna Sinton Taft and a wave of public desire to purchase the increasing popular zoo, took over management. In 1932, the city purchased the zoo and started to run it through the Board of Park Commissioners. This marked the zoo's transition from its period of financial insecurity to its modern state of stable growth and fiscal stability.
In addition to its live animal exhibits, the zoo houses refreshments stands, a dance hall, roads, walkways, and picnic grounds. Between 1920 and 1972, the Cincinnati Summer Opera performed in an open-air pavilion and were broadcast by NBC radio.
In 1987, parts of the zoo were designated as a National Historic Landmark, the Cincinnati Zoo Historic Structures, due to their significant architecture featured in the Elephant House, the Reptile House, and the Passenger Pigeon Memorial.
Animals at the zoo have held several records, including the longest living alligator in captivity at the time (at about 70 years of age), the fastest cheetah in captivity, and the largest Komodo dragon (who died in 2005). The zoo was the first in the United States to put an aye-aye on display, and after losing its last aye-aye in 1993, it finally acquired another in 2011 - a 6-year old transferred from the Duke Lemur Center in North Carolina.
The Cincinnati Zoo has been active in breeding animals to help save species, starting as early as 1880 with the first hatching of a trumpeter swan in a zoo, as well as four passenger pigeons. This was followed in 1882 with the first American bison born in captivity.
In 1986, the zoo established the Carl H. Lindner Jr. Family Center for Conservation and Research of Endangered Wildlife for the purpose of using science and technology to understand, preserve, and propagate endangered flora and fauna and facilitate the conservation of global biodiversity. Its Frozen Zoo plays a major role. In it are stored over 2,500 specimens representing approximately 60 animal and 65 plant species. Terri Roth is CREW's Director.
In the 2010s the zoo built a 8-acre (3.2 ha) Africa exhibit, the largest animal exhibit in its history. Phases I and II, completed in 2010, added an exhibit for cranes and expanded the Cheetah Encounter yard so that the cheetahs had a 40% larger running space. Phase III opened on June 29, 2013 and included a wider vista that offers visitors an opportunity to see African lions, white lions, servals, a bat-eared fox, African wild dogs, and a new cheetah exhibit. A new Base Camp Café, said to be the greenest restaurant in the US, was also added in the 2013 season.
Phase IV, the largest phase of the Africa expansion, opened on June 28, 2014. It introduced a wide savannah with some of Africa's most spectacular hoofstock, such as zebras, gazelles, lesser kudu, impala and giant eland, along with some of the world's largest birds like ostriches, marabou storks, Pink-backed pelican, Rüppell's vultures, Crested guineafowl, Ruddy shelducks, Lappet-faced vultures, and grey crowned cranes.
Phase V, the final phase of the expansion, opened on July 23, 2016, adding an area for Nile hippos, Hippo Cove, which provides both above and below-water viewing. A 34-year-old male named Henry from the Dickerson Park Zoo and a 17-year-old female named Bibi from the St. Louis Zoo joined the zoo. On the morning of January 24, 2017, Bibi gave birth to a six-weeks premature calf. The baby female hippo, named Fiona by zoo staff, is the first hippo to be born at the zoo in 75 years. Fiona was also the first Nile Hippo to ever be captured on an ultrasound image. After intensive care from zoo keepers, veterinarians, and NICU specialists at Cincinnati Children's Hospital, Fiona survived. The story of her trials and success made her an internet celebrity and city hero, and has dramatically increased zoo attendance. Henry's health declined later in 2017 and he was euthanized on October 31.
On July 17, 2017, Eastern Black Rhino baby, Kendi, was born to parents Faru and Seyia. Kendi's birth was captured on camera and can be viewed on the zoo's website. Curator of mammals at the zoo, Christina Gorsuch states, "This calf is only the fifth eastern black rhino born in the last two years in North America." She goes on to say "Every rhino calf born is incredibly important for the population, which includes fewer than 60 in North America. Calves will stay with their mothers for 3-4 years which means that the average female can only have one calf every 5 years."  In 2015, AZA and Species Survival Plan (SSP), determined that parents Faru and Seyia were a good genetic match and recommended that they breed. Faru came to Cincinnati from Atlanta in the summer of 2015 and was introduced to Seyia.
Gorilla World was further expanded in 2016-2017, including the addition of a large indoor building to allow visitors to see the gorillas throughout the year, and Mshindi, a silverback gorilla, came to the zoo from the Louisville Zoo.
In 1931, Robert J. Sullivan permanently loaned the zoo a female gorilla named Susie. Captured in the Belgian Congo, Susie was first sold to a group of French explorers who sent her to France. In August 1929, Susie was transported from Europe to the United States aboard the Graf Zeppelin accompanied by William Dressman. After Susie completed a tour through the United States and Canada with Ringling Bros. and Barnum & Bailey Circus, Sullivan purchased Susie for $4500.00 and loaned her to the zoo. Dressman, who stayed on as Susie's trainer after she was loaned to the zoo, taught her how eat with a knife and fork and orchestrated two performances every day. Susie was so popular that on her birthday on August 7, 1936, more than 16,000 visitors flocked to the zoo. Susie remained one of the most popular animals at the zoo until her death on October 29, 1947. Her body was donated to the University of Cincinnati, where her skeleton remained on display until it was destroyed in a fire in 1974.
On May 28, 2016, Harambe, a 17-year-old, 200-kilogram (440 lb) male Western lowland gorilla, was fatally shot by zoo officials after a three-year-old boy climbed into Harambe's enclosure. The incident was recorded by a bystander and uploaded to YouTube, where the video went viral. Zoo director Thane Maynard stated, "The child was being dragged around ... His head was banging on concrete. This was not a gentle thing. The child was at risk." The shooting was controversial, with some observers stating that it was not clear whether or not Harambe was likely to harm the child. Others called for the boy's parents and/or the zoo to be held accountable for the gorilla's death.
The boy was transported to the hospital with non-life-threatening injuries after being rescued. Police are investigating possible criminal charges, while the parents of the boy defended the zoo's actions. The incident received global publicity; comedian and actor Ricky Gervais, rock guitarist and astrophysicist Brian May, and journalist and television personality Piers Morgan criticized the shooting, while real estate developer and then-candidate for U.S. President, Donald Trump, and zoo director and notable animal expert Jack Hanna both lamented the shooting but defended the zoo's decision to prioritize the boy's safety.Primatologist Frans de Waal neither defended nor condemned the zoo's decision, but described it as a horrible dilemma.
In January 2017, the zoo had its first birth of a hippopotamus in 75 years. Named Fiona, she was born six weeks prematurely and her survival was in doubt. The zoo's efforts to save her and her subsequent improvement to good health provided a viral sensation on the internet.
In 2018 the zoo launched an expansion campaign named "More Home to Roam" with the goal of raising $150 million to be used on developing new attractions and infrastructure. The zoo plans to open Roo Valley and a beer garden in 2020, Rhino Reserve and a 1,800 vehicle parking garage in 2023, and Elephant Trek in 2025. The plan also includes a new entrance to facilitate traffic into the zoo. The additions are also aimed at making the zoo net-zero in terms of waste, water, and energy, making the facilities waste free.
Philanthropists Harry and Linda Fath contributed $50 million to the campaign in June 2018. Previous expansion efforts, such as the Africa exhibit and gorilla exhibit, cost $34 million and $18 million respectively.