Fort Pierce, also spelled Ft. Pierce, is a city in St. Lucie County, Florida, USA. It is known as The Sunrise City. The population was 37,959 at the 2004 census. As of 2008, the population recorded by the U.S. Census Bureau is 41,000.[ ] It is the county seat of St. Lucie County.Fort Pierce is part of the Port St. Lucie, Florida Metropolitan Statistical Area which havepopulation of 400,121.According to the United States Census Bureau, the city has a total area of 20.8 square miles (53.8 km²). 14.7 square miles (38.2 km²) of it is land and 6.0 square miles (15.6 km²) of it (35.00%) is water.