Physical Characteristics. St. Lucie County is on the Atlantic coast and is bordered by Martin, Indian River, and Okeechobee counties. The county has 581.00 square miles of land and 31.19 square miles of water for a total of 612.19 square miles. The average January temperature is 65.1 degrees fahrenheit, and the average August temperature is 81.8 degrees fahrenheit. The average annual rainfall is 49.79 inches.
History. St. Lucie County was established from a portion of Mosquito County in 1844 and named for St. Lucie of Syracuse. The name was changed to Brevard during the 1850s. In 1905 the original name of St. Lucie was restored.
