The Natural History Museum of Los Angeles County is the largest natural and historical museum in the Western United States. The museum is located in Exposition Park, Los Angeles, next to the California Science Center. Its collections include nearly 35 million specimens and artifacts and cover 4.5 billion years of history. This large collection comprises not only of specimens for exhibition, but also vast research collections housed on and offsite.

The museum is associated with two other museums in Greater Los Angeles: the Page Museum at the La Brea Tar Pits in Hancock Park and the William S. Hart Ranch and Museum in Newhall. The three museums work together to achieve their common mission: "to inspire wonder, discovery, and responsibility for our natural and cultural worlds."

NHM opened in Exposition Park, Los Angeles, California, in 1913 as The Museum of History, Science, and Art. The moving force behind it was a museum association founded in 1910. Its distinctive main building with fitted marble walls and domed and colonnaded rotunda, is on The National Register of Historic Places. Additional wings opened in 1925, 1930, 1960, and 1976.

The museum split in 1961 into The Los Angeles County Museum of History and Science and the Los Angeles County Museum of Art (LACMA). LACMA moved to new quarters on Wilshire Boulevard in 1965, and the Museum of History and Science was renamed The Los Angeles County Museum of Natural History. Eventually, the museum renamed itself again, becoming The Natural History Museum of Los Angeles County.

In 2003, the museum began a campaign to transform its exhibits and visitor experience. The museum reopened its seismically retrofitted renovated 1913 rotunda, along with the new "Age of Mammals" exhibition in 2010. Its Dinosaur Hall opened in July 2011. A new Los Angeles history exhibition, "Becoming Los Angeles", opened in 2013. The outdoor Nature Gardens and Nature Lab, which explore L.A. wildlife, also opened in 2013.

In 2024, the museum plans to open a new wing of the museum called the NHM Commons. The commons will be approximately 60,000 square feet consisting of renovations, new constructions, and landscaping; it will be located on the southwest side of the museum. The commons aims to be a community space with a combination of indoor and outdoor experiences including a welcome area, a lobby with a shop, a theater, a café, and a plaza.

The museum maintains research and collections in the following fields:

• Annelida
• Anthropology and Archaeology
• Crustacea
• Echinoderms
• Entomology
• Ethnology
• Herpetology
• History
• Ichthyology
• Invertebrate paleontology
• Malacology
• Mammalogy
• Mineralogy
• Ornithology
• Vertebrate paleontology

The museum has three floors of permanent exhibits. Among the most popular museum displays are those devoted to animal habitats, dinosaurs, pre-Columbian cultures, The Ralph M. Parsons Discovery Center and Insect Zoo, and the new Nature Lab, which explores urban wildlife in Southern California.

The museum's collections are strong in many fields, but the mineralogy and Pleistocene paleontology are the most esteemed, the latter thanks to the wealth of specimens collected from The La Brea Tar Pits.

The museum has almost 30 million specimens representing marine zoology. These include one of the largest collections of marine mammal remains in the world, housed in a warehouse off site, which at over 5,000 specimens is second in size only to that of The Smithsonian.

The museum's collection of historical documents is held in The Seaver Center for Western History Research.

The museum hosts regular special exhibitions which augment its collections and advance its mission. Recent special exhibits have included Mummies and Pterosaurs, both in 2016. The museum has also recently hosted exhibits that incorporate pop culture, such as an exhibit promoting House of the Dragon in 2022. There have also been Los Angeles themed special exhibits such as a Becoming Los Angeles that showcases Los Angeles history through the years, divided up into before 1929 and after 1929. Another example would be the current exhibit titled L.A. Underwater which exhibits almost 40 fossils from the prehistoric time, when the land where L.A. now is, was underwater.

The museum also hosts a butterfly pavilion outside every spring and summer and a spider pavilion on the same site in the fall.

Since 2017, the museum has hosted a special exhibit about P-22, the mountain lion that lived in nearby Griffith Park.

Over the years, the museum has built additions onto its original building. Originally dedicated when The Natural History Museum opened in 1913, the rotunda is one of the museum's most elegant and popular spaces. Lined with marble columns and crowned by a stained glass dome, the room is also the home of the very first piece of public art funded by Los Angeles County, a Beaux-Arts statue by Julia Bracken Wendt entitled Three Muses, or History, Science and Art. This hall is among the most distinctive locales in Los Angeles and has often been used as a filming location.

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  Old east door of The Natural History Museum in 1956
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  Hall of African Mammals
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  Triceratops mount in the Natural History Museum of Los Angeles County
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  Museum rotunda
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  Dinosaur statues along the road leading to the museum

• Official website
• William S. Hart Ranch and Museum
• George C. Page Museum at the La Brea Tar Pits
• Review of the Museum's new Dinosaur Hall at The New York Times, July 19, 2011; Slide show of exhibit
• Digitized materials from the Natural History Museum of Los Angeles County at California Revealed