The smallest national park in the United States is Gateway Arch National Park, located in St. Louis, Missouri. Covering just 91 acres (0.14 square miles), it sits along the banks of the Mississippi River and is dominated by the iconic 630-foot stainless steel arch. In 2026, it remains a unique urban park that shifted from a "National Memorial" to a "National Park" in 2018, a move that remains controversial among some naturalists who prefer the traditional definition of vast wilderness. Globally, the title for "smallest" is often debated, but the Hot Springs National Park in Arkansas was the previous U.S. record holder at 5,500 acres before Gateway Arch took the crown. For visitors, the park's compact size means you can experience the entire site—including the museum, the historic Old Courthouse where the Dred Scott case was heard, and a tram ride to the top of the Arch—in a single afternoon. Its location in the heart of downtown St. Louis makes it the most accessible and "walkable" national park in the entire federal system.