Historic districts in the United States are designated historic districts recognizing a group of buildings, properties, or sites by one of several entities on different levels 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: some have hundreds of structures, while others have just a few.
The U.S. federal government designates historic districts through the United States Department of Interior under the auspices of the National Park Service. Federally designated historic districts are listed on the National Register of Historic Places, but listing usually imposes no restrictions on what property owners may do with a designated property. State-level historic districts may follow similar criteria (no restrictions) or may require adherence to certain historic rehabilitation standards. Local historic district designation offers, by far, the most legal protection for historic properties because most land use decisions are made at the local level. Local districts are generally administered by the county or municipal government.