The United States has 59 protected areas known as national parks. The first national park, Yellowstone, was signed into law by President Ulysses S. Grant in 1872, followed by Sequoia and Yosemite in 1890. The Organic Act of 1916 created the National Park Service "to conserve the scenery and the natural and historic objects and wildlife therein, and to provide for the enjoyment of the same in such manner and by such means as will leave them unimpaired for the enjoyment of future generations." National parks usually have a variety of natural resources over large areas. Many of them had been previously protected as National Monuments by the President under the Antiquities Act before being upgraded by Congress. Seven national parks are paired with a National Preserve, six of which are in Alaska. While administered together, they are considered as separate units and their areas are not included in the figures below. The newest national park is Pinnacles National Park, upgraded in 2013.

Twenty-seven states have national parks, as do the insular areas of American Samoa and the United States Virgin Islands. California has the most, with nine, followed by Alaska with eight, Utah with five, and Colorado with four. The largest national park is Wrangell–St. Elias in Alaska: at over 8 million acres (32,000 km2), it is larger than each of the nine smallest states. The next three largest parks are also in Alaska; the smallest is Hot Springs, Arkansas, at less than 6 thousand acres (24 km2). The total area protected by national parks is approximately 51.9 million acres (210,000 km2), for an average of 895 thousand acres (3,620 km2) but a median of only 317 thousand acres (1,280 km2). The most-visited national park is Great Smoky Mountains, with over nine million visitors in 2011, followed by the Grand Canyon, with over four million; in contrast, fewer than 5,227 people visited the remote Lake Clark.[3] Fourteen national parks are designated World Heritage Sites.