St. Lucie County is located on the central east coast of Florida. St. Lucie County was officially formed on March 14, 1844 and now contains 572 square miles of land area and 116 square miles of water surface.

Originally, Brevard County was part of St. Lucie County and the whole went by the St. Lucie name until the two counties were divided in 1855. A big chunk of the western part of St. Lucie County was cut off to form Okeechobee County in 1917. In 1925, Indian River County was carved out of the northern part of St. Lucie County. Part of the southern section of St. Lucie County went into the creation of Martin County that same year. The county seat is Fort Pierce.