A built object is part of a landmark district when it is recognized as a contributing member to a legally protected district, but is not accorded landmark protection as a single structure. This normally occurs at the local level, depending on the jurisdiction and its landmark laws. In many cases it is a lesser form of protection than local landmark status, meaning that it is less secure legally than an object with individual protection.

The protection arises from the object's contributing role in the larger protected district. It does not amount to an individual landmark designation for that structure.

The district relationship is distinct from local landmark protection of a single object. The relative legal protection depends on the jurisdiction, as described above.