World's first National Park

Yellowstone National Park, 1872 is commonly regarded as the world's oldest national park, however, Bogd Khan Uul almost certainly is the oldest, dating back to 1783, when it was established by the Mongolian government as an area to be kept off limits to exploitation and to be protected for its beauty and nature..

Yellowstone National Park:

Certain "Crown" reserves had been created before that in the British Commonwealth Countries- such as the forest reserve in 1776 on the island of Tobago- however, land belonging to the Monarch and land belonging to the people of a country are not the same thing. Yellowstone National Park was the first park put forth with the concept of national lands belonging jointly to all citizens of a nation, for the enjoyment and preservation of generations to come.

Concerning Yosemite National Park:

A park bill passed both houses of the U.S. Congress, and was signed by President Abraham Lincoln on June 30, 1864, creating the Yosemite Grant.[25] This is the first instance of park land being set aside specifically for preservation and public use by action of the U.S. federal government, and set a precedent for the 1872 creation of Yellowstone as the first national park.