The county’s seat is Fort Pierce. As of the 2019 Census Estimate, St. Lucie County has a population of 328,297. St. Lucie County is included in the Port St. Lucie, FL Metropolitan Statistical Area.
The area was originally inhabited by the Ais tribe, a hunter-gatherer culture whose territory extended from south of the St. John’s river to the St. Lucie Inlet. Spanish explorers frequently encountered the fierce tribe as the Spanish treasure routes ran parallel in order to take advantage of the strong Gulfstream current. The area was given several names by the Spanish including Rio de Ays (later changed to Indian River) as well as Santa Lucia, named after the short-lived late 16th-century Spanish fort that bore its name farther south. The fabled 1715 Spanish treasure fleet sank off the area that is now St. Lucie County, leading to the regional naming of the area as the Treasure Coast. Wikipedia