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As of January 2017, there are 417 units of the National Park System. However, this number is somewhat misleading. For example, Denali National Park and Preserve is counted as two units, since the same name applies to a national park and an adjacent national preserve. Yet Jean Lafitte National Historical Park and Preserve is counted as one unit, despite its double designation. Counting methodology is rooted in the language of a park's enabling legislation. Elsewhere, Fort Moultrie is not counted as a unit because it is considered a feature of Fort Sumter National Monument.
In addition to areas of the National Park System, the National Park Service also provides technical and financial assistance to several affiliated areas authorized by Congress.