6. Port St. Lucie, Florida
> Population growth 2000-2018: 101.4%
> Population in 2000 (Census): 88,769
> Population in 2010 (Census): 164,603
> Population in 2018 (5-yr ACS): 178,778
Port St. Lucie is one of only six cities that had 50,000 or more residents in 2000 and that more than doubled in population over the last two decades. The city’s population grew from 88,769 to 178,778, faster than all but five other cities considered. As is the case in many fast-growing cities, the cost of living in Port St. Lucie is relatively low, 3% less than the national average.