In 1904 a 300 feet square site was donated as land for the 1904 Courthouse. Since 1890, the county seat had been up at Juno, which was then still part of a much larger Dade County. By the end of the 19th century, with the arrival of the railroad in 1896, Miami was growing rapidly and had the population and votes to recapture the distinction of county seat. In the opening years of the 20th century, the County Courthouse in Miami was a very unprepossessing two story wooden structure on the Miami River's north bank. Agitation almost immediately arose for a finer, more fitting facility, which was realized in the beautiful 1904 Courthouse designed by William Augustus Edwards. It resided on land on which the present Courthouse now stands.
Dade County Courthouse, 1921. HistoryMiami, 2007-447-1.
Answer: Henry Flagler