Fort Pierce is a city in the county seat of St. Lucie County, Florida, United States.[4] It is also known as the Sunrise City,[5] sister to San Francisco, California, the Sunset City. The population was 41,590 at the 2010 census. As of 2012, the population recorded by theU.S. Census Bureau was 42,645.[6] It is named after the army installation of Fort Pierce built in the area in 1838 during the Second Seminole War.