-- 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.

"It used to be a nice and quiet community, but everything's changing now. I see new faces everyday," said Sidkey, owner of Sundae's Ice Cream Shoppe & Coffee Bar. "I guess everyone found out our secret."

The secret -- most think it is cheap housing prices -- has made this bedroom 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 last month.

Port St. Lucie experienced the largest population growth for a one-year period beginning in July 2003. It added nearly 12,689 people to reach 118,396 -- a 12 percent jump.

Overall for the past 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 San Francisco, Boston and other large cities in droves.

Gilbert, Ariz., topped the four-year list of fastest-growing cities with at least 100,000 people from April 2000 to July 2004. It grew by more than 46,000 people, or 42 percent, to just more than 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, both 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. "People want to get as much housing as they can for their dollars."

Older industrial cities such as Detroit, Pittsburgh, Cincinnati and Cleveland continued to lose residents.

Port St. Lucie, built on former swampland beginning in the 1960s, saw its population jump 33.4 percent in the past four years. Mayor Bob Minsky said he expects the boom to continue until the population tops 300,000.

He said that each day, 45 people -- young and old -- move to the city and 42 percent of them are coming from the booming cities to the south, where housing prices have become exorbitant for many.

"People like the lifestyle here, and they're willing to commute. They sell their house down south, buy one here and have money left over to put in the bank," Minsky said.

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 significantly less than the median price in the nearby West Palm Beach market of $390,900, where prices rank the ninth highest in the nation.

In Gilbert, the average price for a single-family home was about $220,000. Greg Svelund, Gilbert City spokesman, said many new residents are coming from higher-priced California communities.

In Port St. Lucie, new residents are already happy with their investment here. Ira and Sabina Ratner, who moved last year from Atlantis, said their new home already doubled in value.

"Every time you turn around, there's a new house up," Sabina Ratner said.

Still, all this growth can become unmanageable.

"People have moved up to get out of the congestion, but unfortunately they've made their own congestion," said Esther Heiland, a volunteer at the St. Lucie County Chamber of Commerce.

Port St. Lucie has grown so fast it lacks many of the cultural and social amenities of a large, urban area. There is no shopping mall or downtown, despite years of talk of creating a city center. The only place to get a cup of Starbucks is inside a supermarket; moviegoers have a single choice of theaters. Attractions such as playhouses exist only in the neighboring, older communities of Stuart and Fort Pierce.

But Minsky said the city is catching up with the growth. He said plans are in the works for a performing arts center, an entertainment district and the long-anticipated creation of a downtown.

"This was nothing more than an 80-square-mile swamp when they started it in 1961," Minsky said.

Businesses and housing developments in the Port St. Lucie area have multiplied and spilled farther west, where Shane James works on the plumbing system. Sunset Lakes Early Childhood Center in Miramar, Fla., has grown rapidly as the population of Port St. Lucie has boomed.