Pedro Menéndez de Avilés founded St. Augustine for Spain in 1565 after expelling a French force from nearby Fort Caroline. Timucua communities already occupied northeast Florida, and alliance, coercion, missionization, disease, and warfare transformed their world. The settlement moved several times before stabilizing near its present bayfront. As an administrative, military, and religious center, St. Augustine guarded Atlantic shipping and Spanish claims. Wooden forts and houses repeatedly succumbed to storms, fire, attack, termites, and decay, so little visible architecture survives directly from the sixteenth-century founding.

English privateers and colonial forces attacked the town, prompting construction of the coquina Castillo de San Marcos beginning in 1672. Residents, soldiers, free and enslaved Africans, Native people, craftspeople, clergy, and officials inhabited a walled town with narrow streets and small courtyard houses. A northern defensive line called the Cubo Line crossed the peninsula, and the present City Gate pillars were built in 1808 at its principal entrance. They are Spanish-period masonry features, not the original 1565 gateway and not a complete surviving fortification.

Britain governed East Florida from 1763 to 1783, when Spain regained it. Refugees from the failed New Smyrna colony, including Minorcan, Greek, and Italian families, enlarged the population and shaped local culture. The United States acquired Florida in 1821. The old walls disappeared, buildings changed uses, and Victorian hotels and commercial development altered the city. Henry Flagler's late nineteenth-century resorts introduced grand masonry architecture and tourism. Twentieth-century road projects, restoration, and historical commemoration further transformed how the colonial town was understood and presented.

Public agencies and preservation organizations acquired, researched, and restored numerous properties from the 1930s onward. The state-run preservation program rebuilt several vanished colonial structures on documented lots using archaeology, maps, and historical construction methods. The modern Colonial Quarter continues that interpretive tradition with reconstructed buildings, craft demonstrations, and exhibitions. Genuine coquina structures, restored houses, relocated elements, foundations, and new reconstructions therefore stand close together. The district should not be described as an intact Spanish town preserved unchanged since 1565, despite its legitimate claim as the oldest continuously occupied European-founded city in the continental United States.

The City of St. Augustine, the University of Florida's historic preservation program, the National Park Service, churches, businesses, and private owners share stewardship across the district. Public streets, plazas, and the City Gate are generally free, while the Colonial Quarter, museums, houses, and fort use separate admission systems. Active worship, residences, restaurants, and tourism continue within the historic grid. The district's strongest interpretation distinguishes authentic Spanish and British fabric from later restoration while connecting colonial rivalry to Timucua history, African American freedom, Minorcan migration, American expansion, and the modern heritage economy.