Which national park became the first in the United States in 1872?

Yellowstone National Park became the first national park in the United States in 1872.

President Ulysses S. Grant signed the Yellowstone National Park Protection Act on March 1, 1872. The law reserved more than two million acres in present-day Wyoming, Montana, and Idaho as a public park for the benefit and enjoyment of the people.

Yellowstone's thermal features, including Old Faithful and the Grand Prismatic Spring, helped attract public attention. The Hayden Geological Survey of 1871 produced influential maps, photographs, and reports that supported the idea that the region should be protected rather than privately developed.

The park's creation established a model later used around the world. Yellowstone is not the oldest federally protected landscape in every sense: Yosemite Valley and Mariposa Grove received earlier protection, and Hot Springs Reservation was established in 1832. However, Yellowstone is widely recognized as the first national park created specifically as a large public park for conservation and recreation.