As of 2020, Jacksonville is the most populous city in Florida and the biggest city by area in the contiguous United States. It is situated on the Atlantic coast of the state and is the state's largest metropolis. It serves as the county seat of Duval County, with which the municipal government merged in 1968 to become the City of Jacksonville. It was via consolidation that Jacksonville achieved its enormous size and the majority of its metropolitan population was concentrated inside its municipal boundaries. When the census was taken in 2020, the city's population was 949,611, ranking it as the 12th most populated city in the United States, the most populous city in the Southeast, and the most populous city in the Southern United States other than the state of Texas. The Jacksonville metropolitan area has a population of 1,733,937 people, making it the fourth-largest metropolitan area in Florida.
North of Miami, Jacksonville is located on the St. Johns River in northeast Florida's First Coast area, about 25 miles (40 kilometres) south of the Georgia state border and 328 miles (528 kilometres) north of Atlanta. Communities along the surrounding Atlantic coast, including Jacksonville Beaches, are called "Beaches." In 1564, the French colony of Fort Caroline was established here, becoming one of the oldest European colonies in what is now the continental United States. The region was originally inhabited by the Timucua people, and the French colony of Fort Caroline was established here in 1564. It was under British authority that a village arose at a small place in the river where cattle passed, known by the Seminoles as Wacca Pilatka and by the British as The Cow Ford. After the United States acquired control of Florida from the Spanish in 1821, a platted town was constructed there in 1822, and the town was named after Andrew Jackson, who served as first military governor of the Florida Territory and as the nation's seventh President from 1845 to 1849.
After years of development, Jacksonville has emerged as a significant military and commercial deep-water port since the late nineteenth century. As a result of its riverine position, the Naval Station Mayport, the Naval Air Station Jacksonville, the United States Marine Corps Blount Island Command, and the Port of Jacksonville, Florida's third biggest seaport, are all within easy reach. Together with the adjacent Naval Submarine Base Kings Bay, Jacksonville's military bases constitute the third biggest military presence in the country. Services like as banking, insurance, healthcare, and logistics are all important contributors to the local economy. Tourism is vital in the Jacksonville region, as it is in all of Florida, and is particularly important in the golfing community. Jacksonville residents are referred to as "Jacksonvillians" or "Jaxsons" by some (also spelled "Jaxons").