Florida (i /ˈflɒrɪdə/) is a state of the United States. It is located in the Southeastern United States, bordering Alabama to the northwest and Georgia to the north. Much of the land mass of the state is a large peninsula with the Gulf of Mexico to the west, the Atlantic Ocean to the east and the Caribbean to the south. Florida was admitted as the 27th U.S. state in 1845, after over three hundred years of settlement and colonization.

With an area of 65,758 square miles (170,306 km2), it is ranked 22nd in size among the 50 U.S. states. Florida has the longest coastline in the Contiguous United States encompassing approximately 1,350 miles (2,170 km). The state has four large urban areas, a number of smaller industrial cities, and many small towns.

Florida is nicknamed the "Sunshine State" because of its generally warm climate—subtropical in the northern and central regions of the state, with a true tropical climate in the southern portion. The United States Census Bureau estimates that the state population was 18,537,969 in 2009, ranking Florida as the fourth most populous state in the U.S. Tallahassee is the state capital, Jacksonville is the largest city, and the South Florida metropolitan area is the largest metropolitan area.

Archaeological research indicates that Florida was first inhabited by Paleo-Indians, the first human inhabitants of the Americas, perhaps as early as 14 thousand years ago. The region was continuously inhabited through the Archaic period, and after about 500 BC the previously relatively uniform Archaic culture began to fragment into local cultures. By the 16th century, the earliest time for which there is a historical record, major Native American groups included the Apalachee (of the Florida Panhandle), the Timucua (of northern and central Florida), the Ais (of the central Atlantic coast), the Tocobaga (of the Tampa Bay area), the Calusa (of southwest Florida) and the Tequesta (of the southeastern coast).

Florida was the first part of what is now the continental United States to be visited by Europeans. The earliest known European explorers came with the Spanish conquistador Juan Ponce de León, who spotted the peninsula on April 2, 1513. According to his chroniclers, Ponce de León named the region La Florida ("flowery land") because it was then the Easter Season, known in Spanish as Pascua Florida (roughly "Flowery Easter"), and because the vegetation was in bloom. It is possible Juan Ponce de León was not the first European to reach Florida, however; reportedly, at least one indigenous tribesman whom he encountered in Florida in 1513 spoke Spanish. From 1513 onward, the land became known as "La Florida," although after 1630 and throughout the 1700s, Tegesta (after the Tequesta tribe) was an alternate name of choice for the Florida peninsula following publication of a map by the Dutch cartographer Hessel Gerritsz in Joannes de Laet's History of the New World.

Over the following century, both the Spanish and French established settlements in Florida with varying degrees of success. In 1559, a colony at present-day Pensacola was established by Don Tristán de Luna y Arellano as the first European settlement in the continental United States. It was abandoned by 1561 due to hurricanes, famine and warring tribes, and was not re-inhabited until the 1690s. French Huguenots founded Fort Caroline in modern-day Jacksonville in 1564, but in the following year, the fort was conquered by forces from the new Spanish colony of St. Augustine (called San Agustín in Spanish). The Spanish maintained tenuous control over the region by converting the local tribes, briefly with Jesuits and later with Franciscan friars. The local leaders (caciques) demonstrated their loyalty to the Spanish by converting to Roman Catholicism and welcoming the Franciscan priests into their villages.

The area of Spanish Florida diminished with the establishment of English colonies to the north and French colonies to the west. The English weakened Spanish power in the area by supplying their Creek and Yamaseee allies with firearms and urging them to raid the Timucuan and Apalachee client-tribes of the Spanish. The English attacked St. Augustine, burning the city and its cathedral to the ground several times, while the citizens hid behind the walls of the Castillo de San Marcos.

Florida was attracting a large number of Africans and African Americans from British-occupied North America who sought freedom from slavery. Once in Florida, the Spanish Crown converted them to Roman Catholicism and gave them freedom. Those ex-slaves settled in a community north of St. Augustine, called Gracia Real de Santa Teresa de Mose, the first freedom settlement of its kind in what became the United States. Many of those slaves were also welcomed by Creek and Seminole Native Americans who had established settlements there at the invitation of the Spanish government.

Great Britain gained control of Florida diplomatically in 1763 through the Peace of Paris. The British divided the colony into East Florida, with its capital at St. Augustine, and West Florida, with its capital at Pensacola. Britain tried to develop the Floridas through the importation of immigrants for labor, but this project ultimately failed. Spain regained the Floridas after Britain's defeat by the American colonies and the subsequent Treaty of Versailles in 1783, continuing the division into East and West Florida. They offered land grants to anyone who settled in the colonies, and many Americans moved to them.

After settler attacks on Indian towns, Seminole Indians based in East Florida began raiding Georgia settlements, purportedly at the behest of the Spanish. The United States Army led increasingly frequent incursions into Spanish territory, including the 1817–1818 campaign against the Seminole Indians by Andrew Jackson that became known as the First Seminole War. Following the war, the United States effectively controlled East Florida. In 1819, by terms of the Adams-Onís Treaty, Spain ceded Florida to the United States in exchange for the American renunciation of any claims on Texas that they might have from the Louisiana Purchase and $5 million.