The boundaries of an NHLD typically include contributing properties that may themselves be listed distinctly as a
National Historic Landmark or on the National Register of Historic Places but may also include non-contributing properties. The
U.S. federal government designates historic districts through the
National Park Service, a division of the
U.S. Department of the Interior. Once designated an NHL District, districts often become cultural destinations and generate economic benefits for the communities from history-related tourism. NHLDs often qualify for preservation grant monies but dramatic or negative change to them can impact their integrity and create cause for concern over the loss of NHLD designation. These threats can come from development or climate change as evidenced most recently with the catastrophic damage to the Lahaina NHLD from wildfires. One of the largest NHLDs is the island of
Nantucket, Massachusetts, at over 30,000 acres; some are much smaller, including the Cobblestone National Historic Landmark District in
New York state, which is under one acre in size. ==Distribution by state==