Florida became an organized territory of the United States on March 30, 1822. The Americans merged East Florida and West Florida (although the majority of West Florida was annexed to Territory of Orleans and Mississippi Territory), and established a new capital in Tallahassee, conveniently located halfway between the East Florida capital of St. Augustine and the West Florida capital of Pensacola. The boundaries of Florida's first two counties, Escambia and St. Johns, approximately coincided with the boundaries of West and East Florida respectively.

This area was the first mainland realm of the United States to be settled by Europeans. Thus, 1513 marked the beginning of the American Frontier. From that time of contact, Florida has had many waves of colonization and immigration, including French and Spanish settlement during the 16th century, as well as entry of new Native American groups migrating from elsewhere in the South, and free blacks and fugitive slaves, who in the 19th century became allied with the Native Americans as Black Seminoles. Florida was under colonial rule by Spain, France, and Great Britain during the 18th and 19th centuries before becoming a territory of the United States in 1821. Two decades later, in 1845, Florida was admitted to the union as the 27th US state. Since the 19th century, immigrants have arrived from Europe, Latin America, Africa and Asia.