National Historic Landmark

A National Historic Landmark (NHL) is a building, site, structure, object, or district with historical importance. The United States government marks them as NHLs only if they have high historical significance. Out of more than 80,000 places on the National Register of Historic Places only about 2,430 are NHLs.
A National Historic Landmark District (NHLD) is a historic district that is recognized as an NHL. It may include contributing properties that have buildings, structures, sites or objects, and it may include non-contributing properties.
History.
On October 9, 1960, Secretary of the Interior Fred Andrew Seaton announced 92 properties as NHLs. The first of these was a political nomination, Sergeant Floyd Grave and Monument in Sioux City, Iowa as officially designated on June 30 of that year, but for various reasons the public announcement of the first several NHLs was delayed.
Criteria.
NHLs are designated by the United States Secretary of the Interior because they are:
Overview of current NHLs.
Of the 2,442 or so current NHLs, 3 states, Pennsylvania, Massachusetts, and New York account for nearly 25 percent of the nation's NHLs. In addition to these states, cities within these states, Boston, Philadelphia, and New York City (each separately) alone have more NHLs than 40 out of the 50 states. There are NHLs in all 50 states. There are 74 in the District of Columbia, 15 in Puerto Rico and other U.S. commonwealths and territories, five in U.S.-associated states such as Micronesia, and one in Morocco.
There are 128 ships or shipwrecks that are NHLs.
Other.
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. The National Historic Landmark Stewards Association is a friends' group of owners and managers who 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.