It is believed that the name "St. Lucie" was first introduced to the area by the Spanish. In 1565 Fort Santa Lucia was built by the Spanish, at the Jupiter Inlet. Construction for this fort began on December 13th, the feast day of the Roman Catholic Saint Lucia. Pedro Menendez de Aviles established a colony in 1567 called "Santa Lucia" somewhere between Vero Beach and Stuart. Old Spanish maps identify the area as Santa Lucia.

The current Saint Lucie County was known as East Florida in 1810. In 1821 the area was renamed St. Johns County. St. Johns was split into several counties in 1840 and this area became Mosquito County. Ten years later the Mosquito County area was slashed into two new counties and our area became St. Lucie for the first time. Thirty more years pass and in 1880 the borders were again changed and St. Lucie became Brevard County. On July 1, 1905 St. Lucie County, Florida was established with Fort Pierce as the county seat. Portions were stripped away over the years, first in 1917 western acres were taken away to become Okeechobee County. In 1925 a northern chunk of land was removed and became Indian River County and the southern part of St. Lucie as well as a portion of Palm Beach County became Martin County that same year.