Old City Historic District in the context of "Independence National Historical Park"

Historic districts in the United States are designated historic districts recognizing a group of buildings, archaeological resources, or other properties as historically or architecturally significant. Buildings, structures, objects, and sites within a historic district are normally divided into two categories, contributing and non-contributing. Districts vary greatly in size and composition: a historic district could comprise an entire neighborhood with hundreds of buildings, or a smaller area with just one or a few resources.

Historic districts can be created by federal, state, or local governments. At the federal level, they are designated by the National Park Service and listed on the National Register of Historic Places; this is a largely honorary designation that does not restrict what property owners may do with a property. State-level historic districts usually do not include restrictions, though this depends on the state. Historic districts created by local municipalities, however, almost always protect historic properties by regulating alterations, demolition, or new construction within the district.