I went to St. Joseph, located in Gulf County, on 2/6/2017. I completed Gulf County today. Yayee!
According to the ghost town website,
In the early 1800s, St. Joseph was the largest town in Florida with 6000 residents. It served as a seaport, which proved to be its demise when in 1841 a ship docked with occupants carrying yellow fever. Over 75% of the town died of the disease and the rest of the population fled. Hurricanes have since destroyed the remains.