St. Lucie County is located in the southeastern portion of the U.S. state of Florida. As of the 2020 census, the population was 329,226. The county's seat is Fort Pierce, while the largest city is Port St. Lucie, making up 62% of the county's population. St. Lucie County is the principal county of the Port St. Lucie, FL Metropolitan Statistical Area.

Fort Pierce is a city in and the county seat of St. Lucie County, Florida, United States. The city is part of the Treasure Coast region of Atlantic Coast Florida. It is also known as the Sunrise City. Per the 2020 census, the population was 47,297.