<P> Dade County was created on January 18, 1836, under the Territorial Act of the United States . The county was named after Major Francis L. Dade, a soldier killed in 1835 in the Second Seminole War, at what has since been named the Dade Battlefield . At the time of its creation, Dade County included the land that now contains Palm Beach and Broward counties, together with the Florida Keys from Bahia Honda Key north and the land of present - day Miami - Dade County . The county seat was originally at Indian Key in the Florida Keys; then in 1844, the County seat was moved to Miami . The Florida Keys from Key Largo to Bahia Honda were returned to Monroe County in 1866 . In 1888 the county seat was moved to Juno, near present - day Juno Beach, Florida, returning to Miami in 1899 . In 1909, Palm Beach County was formed from the northern portion of what was then Dade County, and then in 1915, Palm Beach County and Dade County contributed nearly equal portions of land to create what is now Broward County . There have been no significant boundary changes to the county since 1915 . </P> <P> The third - costliest natural disaster to occur in the United States was Hurricane Andrew, which hit Miami in the early morning of Monday, August 24, 1992 . It struck the southern part of the county from due east, south of Miami and very near Homestead, Kendall, and Cutler Ridge (now the Town of Cutler Bay). Damages numbered over US $25 billion in the county alone, and recovery has taken years in these areas where the destruction was greatest . This was the costliest natural disaster in US history until Hurricane Katrina struck the Gulf region in 2005 . </P> <P> On November 13, 1997, voters changed the name of the county from Dade to Miami - Dade to acknowledge the international name recognition of Miami . Voters were acting pursuant to home rule powers granted to Dade County, including the ability to change the name of the county without the consent of the Florida Legislature . The change in name also addressed a source of public dissatisfaction with the name "Dade" which was chosen to honor of Francis L. Dade, who had been killed in the Dade Massacre in the 1830s . The massacre did not occur in South Florida, but in the west central part of the state, in present - day Sumter County, near Bushnell . There is also a Dade City, which is closer to the site of the massacre . </P> <P> According to the U.S. Census Bureau, the county has a total area of 2,431 square miles (6,300 km), of which 1,898 square miles (4,920 km) is land and 533 square miles (1,380 km) (21.9%) is water . It is the third - largest county in Florida by land area and second - largest by total area . Most of the water is in the Biscayne Bay, with another significant portion in the adjacent waters of the Atlantic Ocean . </P>

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