National Park Service
The United States National Park system encompasses approximately 83.6 million acres, of which more than 4.3 million acres remain in private ownership. The largest area is Wrangell - St Elias National Park and Preserve, Alaska. At 13,200,000 acres it is 16.3 percent of the entire system. The smallest unit in the system is Thaddeus Kosciuszko National Memorial, Pennsylvania, at 0.02 of an acre.
See also : List of United States National Parks