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About half of the National Historic Landmarks are privately owned. The National Historic Landmarks Program relies on suggestions for new designations from the National Park Service, which also assists in maintaining the landmarks. A friends' group of owners and managers, the National Historic Landmark Stewards Association, works to preserve, protect and promote National Historic Landmarks.
If not already listed on the National Register of Historic Places, an NHL is automatically added to the Register upon designation. About three percent of Register listings are NHLs.
Read more about this topic: National Historic Landmark