[ethbr1]

To cite sources:

>> On March 1, 1872, President Ulysses S. Grant signed The Act of Dedication law that created Yellowstone National Park. https://en.m.wikipedia.org/wiki/Yellowstone_National_Park#Hi...

I believe the Yellowstone claim is based on the fact that it was the first park explicitly declared for the benefit of the public by a federal government.

[bombcar]

There are national park-like things that existed before, but they were often technically owned by the King or somesuch.