Which U.S. National Park Service park was the first national park east of the Mississippi River?

Acadia National Park was the first U.S. national park east of the Mississippi River.

Congress created the park as Lafayette National Park on February 26, 1919. It occupied portions of Maine's Mount Desert Island and nearby lands, following years of work by conservationists including George B. Dorr. The park was renamed Acadia National Park in 1929.

Its federal history began earlier, when President Woodrow Wilson proclaimed Sieur de Monts National Monument in 1916. That monument was administered by the newly created National Park Service and formed the foundation for the later national park.

Acadia protects rocky coastlines, forests, ponds, islands, and granite mountains along the Maine coast. Cadillac Mountain is the highest point on the North Atlantic seaboard. A common mix-up is to identify Shenandoah or Great Smoky Mountains as the first eastern national park; both were established later than Acadia.