The Adirondack Park is a publicly protected, elliptical area encompassing much of the northeastern lobe of Upstate New York. It is the largest park and the largest state-level protected area in the contiguous United States, and the largest National Historic Landmark. The park covers some 6.1 million acres (2.5×106 ha), a land area roughly the size of Vermont and greater than the National Parks of Yellowstone, Yosemite, Grand Canyon, Glacier, and Great Smoky Mountains combined.

The Adirondack Park boundary, commonly referred to as the ‘Blue Line,’ contains the entire Adirondack Mountain range, as well as some surrounding areas, all within the state of New York. The park includes all of Hamilton and Essex counties, as well as considerable portions of Clinton, Franklin, Fulton, Herkimer, St. Lawrence, and Warren counties and small portions of Lewis, Oneida, Saratoga, and Washington counties as well. (The Clinton County towns of Altona and Dannemora, despite being entirely within the park boundary, are specifically excluded from the park by statute, due to the large prison facilities in both towns.)

Not all of the land within the park is owned by the state, although new sections are frequently purchased or donated. State land comprises 2.7 million acres (1.1×106 ha), about 45% of the park’s area, including the highest peaks in New York State, as well as Mount Marcy, the highest elevation in the state. About 1 million acres (400,000 ha) of this is classified as wilderness, with most of the remainder managed under the somewhat less stringent wild forest classification. Villages and hamlets comprise less than 1% of the area of the park; the remaining area of more than 3 million acres (1.2×106 ha) is privately held but is generally sparsely developed.[3] There is often no clear demarcation between state, private, and wilderness lands in the park. Signs marking the Adirondack Park boundary can be found on most of the major roads in the region, but there are no entrance gates and no admission fee.