Facts & Stats. Between 2000 and 2010, St. Lucie was one of the fastest growing counties in the U.S. With a total population increase of more than 80,000 during that time frame, the demographics and labor force are diversifying into a more knowledge based economy. As of the 2013 Census Estimate, St. Lucie County is at a population of 286,832. Incorporated in 1905, St. Lucie County is included in the Port St. Lucie, FL Metropolitan Statistical Area, which is also included in the Miami-Fort Lauderdale-Port St. Lucie, FL Combined Statistical Area.