<Tr> <Th> Public transit access </Th> <Td> Smithsonian or Federal Triangle </Td> </Tr> <Tr> <Th> Website </Th> <Td> www.mnh.si.edu </Td> </Tr> <P> The National Museum of Natural History is a natural - history museum administered by the Smithsonian Institution, located on the National Mall in Washington, D.C., United States . It has free admission and is open 364 days a year . In 2016, with 7.1 million visitors, it was the fourth most visited museum in the world and the most visited natural - history museum in the world . Opened in 1910, the museum on the National Mall was one of the first Smithsonian buildings constructed exclusively to hold the national collections and research facilities . The main building has an overall area of 1,500,000 square feet (140,000 m) with 325,000 square feet (30,200 m) of exhibition and public space and houses over 1,000 employees . </P> <P> The museum's collections contain over 126 million specimens of plants, animals, fossils, minerals, rocks, meteorites, human remains, and human cultural artifacts . In 2016 it was the second most visited of all of the Smithsonian museums . It is also home to about 185 professional natural - history scientists--the largest group of scientists dedicated to the study of natural and cultural history in the world . </P>

When was the national museum of natural history built