St. Augustine is the oldest continuously inhabited European-established settlement in the continental United States.
Spanish admiral Pedro Menéndez de Avilés founded St. Augustine in 1565, naming it San Agustín after the feast day on which his expedition first sighted the Florida coast. The settlement predates the English colony at Jamestown by 42 years and Plymouth Colony by 55 years.
Spain established St. Augustine as a defensive and administrative center in Florida. The city changed hands between Spain, Britain, Spain again, and the United States before Florida became a U.S. territory in 1821. Its long history is visible in landmarks such as Castillo de San Marcos, whose construction began in 1672.
The wording matters: St. Augustine is not the oldest human settlement in North America, nor the oldest Indigenous settlement. Its distinction refers specifically to continuous habitation by a European-established settlement in the continental United States.