Maritime history of Florida
Spain ceded Florida to the United States as part of the Adams–Onís Treaty of 1819, and Florida became a U.S. territory in 1821. Coastal trade with other markets continued to expand and towns like Jacksonville, Pensacola and Tampa became important ports. After becoming a U.S. territory, the federal government began building a series of lighthouses as aids to navigation along the coasts of Florida to mark dangerous headlands, shoals, bars and reefs.
Key West
On March 25, 1822, Lt. Commander Matthew C. Perry sailed the schooner "Shark" to Key West and planted the U.S. flag, claiming the Keys as United States property. No protests were made over the American claim on Key West, so the Florida Keys became the property of the United States.