Key West developed on the ancestral maritime world of Indigenous peoples and on an island known to Spanish navigators as Cayo Hueso. The United States claimed Florida in 1821, and American settlement accelerated after businessman John Simonton acquired the island. Key West was incorporated in 1828. Its deep harbor and position near the Florida Straits supported wrecking, fishing, salt production, shipping, and naval activity. Streets and lots filled with frame houses, warehouses, shops, churches, cisterns, and docks adapted to a hot climate and scarce fresh water.

Nineteenth-century wrecking courts and salvors profited from ships lost on the Florida Reef, making Key West one of the young nation's wealthiest communities per capita for a time. Fortifications and the Navy strengthened the federal presence, especially during the Civil War. Cigar manufacturing later drew Cuban owners and workers and connected Key West closely to Havana and Cuban independence movements. Bahamian migrants, Black residents, sailors, merchants, and laborers created neighborhoods and institutions whose history complicates a tourism image focused only on wealthy houses and famous writers.

Fire repeatedly reshaped the wooden city. The Great Fire of 1886 swept through the commercial core, destroying hundreds of buildings, including numerous cigar factories, before new construction filled the damaged blocks. Builders used timber framing, clapboards, shutters, porches, high ceilings, and raised floors, while some prominent civic, religious, and commercial structures employed brick or stone. Rail and highway connections gradually reduced maritime isolation. The Depression, military investment, fishing, and twentieth-century tourism produced additional layers, as did Cuban migration and the city's reputation for artistic and social independence.

Mallory Square occupies a working waterfront area historically associated with docks, warehouses, the naval station, commerce, and immigration rather than a purpose-built historic plaza. Surviving buildings such as the Custom House and later adaptive reuse frame a public space now famous for nightly sunset gatherings. Elsewhere in Old Town, extensive nineteenth- and early twentieth-century fabric survives, but individual buildings may have been moved, raised, extended, restored, or reconstructed after fire and hurricanes. Bright paint, retail conversion, guesthouses, and modern storm protection reflect continued occupation, not an untouched streetscape.

Key West's local Historic Architectural Review Commission regulates changes within designated historic areas, while public agencies, nonprofits, churches, businesses, and homeowners manage individual resources. Streets and Mallory Square are generally free to enter, but museums, tours, and events set separate prices and hours. Preservation faces hurricanes, flooding, salt, heat, insurance costs, intensive tourism, and housing pressure. The district's value lies in its living urban pattern and layered communities, not in a claim that every façade is original. Visitors should distinguish authentic structures, rehabilitated interiors, relocated houses, and modern construction designed to fit historic surroundings.