PORT ST. LUCIE, Fla. -- Michael Sidkey's 4-year-old ice cream shop used to sit in a sleepy strip mall along a two-lane road on the western edge of town.
These days, the road is six lanes, bustling with midday traffic. Businesses and housing developments have multiplied and spilled farther west. And people keep moving here in record numbers, despite the onslaught of two hurricanes last year.
''I guess everyone found out our secret," Sidkey said.
The secret -- most think it's low housing prices -- has made this community about 50 miles north of West Palm Beach the fastest-growing large city in the nation, according to census figures for 2003-2004 released yesterday.
Port St. Lucie experienced the largest population growth for a one-year period beginning in July 2003. It added 12,689 people to reach 118,396, a 12 percent jump.
Overall for the last four years, the census numbers show new residents flocking to midsize cities in Florida, Arizona, Nevada, and California. Hurt by skyrocketing housing prices, people are leaving Boston, San Francisco, and other large cities in droves.
Gilbert, Ariz., topped the four-year list of fastest-growing cities with 100,000 people from April 2000 to July 2004. It grew by more than 46,000 people, or 42 percent, to just over 156,000 residents.
Next on the list ranked by percentage gain was Miramar, Fla., followed by North Las Vegas, Nev., and Port St. Lucie. Rounding out the top 10 were Roseville, Calif.; Henderson, Nev.; Chandler, Ariz.; Cape Coral, Fla.; and Rancho Cucamonga and Irvine in California.
''People like to live in smaller places, and a lot of it's propelled by the sharp spike in housing costs in the inner and more attractive cities," said William H. Frey, a demographer at the Brookings Institution in Washington.
Port St. Lucie saw its population jump 33.4 percent in the last four years. Mayor Bob Minsky said he expects the boom to continue until the population tops 300,000: ''People like the lifestyle here."
The median price of a home in the Port St. Lucie area was $253,200 in May 2005. That is a 35 percent jump over the previous year but lower than the median price of $390,900 in West Palm Beach, where prices rank the ninth-highest in the nation.
''This was nothing more than an 80-square-mile swamp when they started it in 1961," Minsky said.