Texas is getting bigger, at least in terms of population growth in its metropolitan areas, with Houston gaining more residents over the past decade than any of the nation's other 365 cities, according to a new study.

Between 2000 and 2010, the Greater Houston metropolitan area grew by a whopping 1.2 million people, increasing by more than 123,000 individuals per year over the decade.

"Houston's growth represents more people than the population growth in the New York and Chicago metropolitan areas combined during the past decade," said Michael Emerson, co-director of the Kinder Institute for Urban Research at Rice University. [See full list of fastest-growing cities]

Overall, the rate of U.S. population growth has slowed in recent decades. For instance, between 2000 and 2010, the U.S. population grew by 9.7 percent, compared with a 13.2 percent increase between 1990 and 2000. As of today, U.S. population stands at 311,754,919 individuals, according to the U.S. Census Bureau.

The Dallas-Fort Worth area wasn't far behind Houston, gaining just 21,000 fewer people over the decade than Houston.

"As of 2011, the population increases in the Houston and Dallas-Fort Worth metropolitan areas have catapulted the two cities into the No. 5 (Houston) and No. 4 (Dallas-Fort Worth) largest metropolitan areas in the United States," Emerson added.

The only other metropolitan area to grow by more than 1 million people over the 2000-2010 period was Atlanta, the nation's ninth-largest city. [Happiest U.S. Cities]

Many factors may be responsible for Houston's growth, Emerson said, including its closeness to Latin America, its emergence as a major destination for immigrants from around the world, the area’s pro-business policies, the low cost of living, significant job growth and its location in the fastest-growing state in the nation.

The South in general seems to have opened the floodgates lately, continuing a trend over the past several decades of concentrated population growth in the U.S. South and Southwest, the researchers said.

Of the 15 metropolitan areas that added the most people over the past decade, only New York (No. 7) and Seattle (No. 15) are not in the South or the Southwest.

"A significant portion of the population growth in these Southern and Southwestern metropolitan areas is not due to the relocation of Americans from colder climates, but to the influx of immigrants moving directly into these Southern and Southwestern metropolitan areas," Emerson said. "This is the secret of Houston’s phenomenal growth over the past decade. It comes not primarily from relocating or retiring Americans, but from first-generation immigrants and from their children born in Houston."

This article was reprinted with permission from LiveScience.

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