Janice Turner has seen Olive Branch flourish over the last two decades. A small town became Mississippi's ninth-largest city as thousands of people relocated across the state line from Memphis.

The 51-year-old paralegal has spent her life in Olive Branch, 20 miles south of Memphis. Back in 1960 the population added up to only 642, according to the U.S. Census Bureau. Turner remembers when visitors to the public library needed merely to drop a slip in a wooden box to borrow books; the expanded 19,000-sq.-ft. library is now Mississippi's second-busiest. Traffic is heavier all over town. It used to take five minutes to drive from one end to the other and can now take 30 minutes during peak hours, she says.

Over the last two decades the population of Olive Branch has exploded by 838 percent. In 1990 residents numbered 3,567. A decade later they totalled 21,054. By 2010, there were 33,484, according to data from the Decennial Census.

In a ranking completed by location analysis company Gadberry Group for Businessweek.com, the Olive Branch area is not only the fastest-growing town in Mississippi, but the fastest growing city in the U.S. The ranking is based on such factors as growth in the number of households within city limits and surrounding areas over the decade and from 2009 to 2010, plus average length of residency and average household income.

Keys: income and length of residence

In addition to household growth, says Gadberry Group principal Larry Martin, "income is one of the primary demographics that define an area's attractiveness. Length of residence is important as a corroborating variable for growth. If an area is truly growing, then the average length of residence should be shorter than an area with flat growth."

From 2000 to 2010, the U.S. population grew by 9.7 percent, according to results from the latest census, but places such as Olive Branch grew at a considerably quicker pace. Other high-growth areas include Keller, Tex., Ellicott City, Md., and South Jordan, Utah, according to Gadberry Group.

"I believe that jobs, affordable housing, a sense of security, and a sense of community are primary drivers," says Martin. "When all of these conditions exist, the odds of growth are high. When none exist, the odds of decline are high."

Not surprisingly, the unemployment rate in these fast-growing cities is lower than the average for their states. Olive Branch's jobless rate in March was 7.5 percent, compared with Mississippi's average 10.2 percent. In Texas, Keller's 6.3 percent rate contrasts with a statewide average of 8.1 percent.

Job growth, surfeit of housing

Fast-growing cities and states are vulnerable to the perils of overbuilding. The effects of the housing bubble are most evident today in Nevada—America's fastest-growing state from 2000 to 2010—which now suffers from the country's highest foreclosure rate.

Today, Olive Branch has 14,724 households, according to Gadberry. Because its population grew faster than the national rate, about 30 percent of the city's homes were built after 2000, far above the national rate of 11 percent, according to data from the U.S. Census Bureau. The city's numbers indicate that from 500 to 700 single-family building permits were issued every year from 2002 to 2006. Since 2008, that number has dropped to about 100 annually.

Olive Branch had a relatively high level of 10.8 months of housing supply in March, according to Pam Simpson, associate broker at Bob Leigh & Associates Realtors, compared to a national rate of about 8 months. (In 2010, its inventory level averaged 8.9 months.) But with foreclosures accounting for 6.4 percent of inventory and one-third of all home sales, the median list price has dropped by about 20 percent, to $175,000, since April 2008, according to data from Zillow.com.

Despite the inconveniences associated with expansion, interest in the city remains keen because of DeSoto County's highly ranked school system, as well as Olive Branch's greater real estate values and lower crime rate in comparison with its urban neighbor. Most residents want to preserve the small town feel, but Page says the city's population might eventually surpass 100,000. Growth has slowed since the recession, says Simpson, but "it's still an attractive place and a place that people are looking to move to."

The list

Here are America's 10 fastest growing cities: