Thursday is the United States National Park Service's 100th birthday.

On Aug. 25, 1916, then-President Woodrow Wilson officially made the service a federally managed bureau aimed at promoting and regulating certain special areas "to conserve the scenery and the natural and historic objects and the wild life therein and to provide for the enjoyment of the same in such manner." Today, the parks are a huge system of land anyone can enjoy.

To celebrate the landmark 100th anniversary of the creation of the National Park Service, read up on the land and species it protects. Here are 17 facts to share Thursday, mostly collected from the National Park Service Overview:

In 1920, about 1 million people visited the parks. In 2015, more than 307 million did.

The parks are spread out over 84 million acres.

There are 59 national parks. 

GettyImages-182597954 A tourist takes a picture of Mount Rushmore National Memorial from outside the park on Oct. 1, 2013 in Keystone, South Dakota. Photo: Getty Images

The service officially allowed female rangers starting in 1917. The first was named Clare Marie Hodges.

The Blue Ridge Parkway is 469 miles long. 

The first national park was Yellowstone. 

The parks contain more than 18,000 miles of trails.

GettyImages-588665544 A Perseid meteor streaks across the sky above Inspiration Point early on Aug. 12 in Bryce Canyon National Park, Utah. Photo: Getty Images

The Great Smoky Mountains National Park was the most-visited one in 2015, followed by the Grand Canyon and Rocky Mountain parks.

The state with the most national parks is California.

Death Valley National Park was the setting for Tatooine in "Star Wars." 

The park system includes battlefields, monuments and seashores, as well. There are about 400 total areas protected by the service.

RTR1ZOPW A rainbow forms at the foot of Bridalveil Fall in Yosemite National Park in California April 19, 2008. Photo: Reuters

The parks service has more than 20,000 employees.

Endangered species living in the parks include the Ozark hellbender, the Kemp's Ridley sea turtle and the American pika.

The Smokies have been called the salamander capital of the world.

Fourth graders can visit the national parks for free this year though a government program. If you don't know one, you can stop by on Sept. 24 or Nov. 11 for free admission.

There were no wolves in Yellowstone between the 1926 and 1995.

Roosevelt once said that being in Yosemite was like "lying in a great solemn cathedral, far vaster and more beautiful than any built by the hands of man."