Florida is not in any immediate risk of sinking into the ocean, but it does face long-term risks of substantial subsidence due to its geology. Florida receives a great deal of rain, and mostly sits atop salt and gypsum rocks, along with a substantial portion of limestone, both of which are soluble in water. The dissolution of rock, combined with the draining of Florida's swamps, creates large risks.
Florida is has one of the lowest average elevations in the United States at 100 feet, and it is also the flattest state. This low, flat landscape does put it at risk when any overall subsidence or decrease in elevation occurs, according to the United States Geological Survey. Most of the subsidence in Florida so far has not been gradual and large-scale, but rather small and catastrophic in the form of sinkholes. These sudden collapses of relatively small areas are dangerous to people and structures, but do not significantly affect the overall elevation of the land.
The overall wetness of Florida is protective against large-scale subsidence because groundwater supplies are quickly replenished. This stands in contrast to dry places like the San Joaquin Valley in California, where the withdrawal of groundwater for farming has caused the land to sink by as much as 30 feet in places.