WASHINGTON - America's population center is edging away from the Midwest, pulled by Hispanic growth in the Southwest, according to census figures. The historic shift is changing the nation's politics and even the traditional notion of the country's heartland - long the symbol of mainstream American beliefs and culture.

The West is now home to the four fastest-growing states - Nevada, Arizona, Utah, and Idaho - and has surpassed the Midwest in population, according to 2010 figures. California and Texas added to the southwestern population tilt, making up more than one-fourth of the nation's total gains since 2000.

When the Census Bureau announces a new mean center of population next month, geographers believe it will be placed in or around Texas County, Mo. That would put the center at the outer edge of the Midwest on a path to leave the region by midcentury.

"The geography is clearly shifting, with the West beginning to emerge as America's new heartland," said Robert Lang, a sociology professor at the University of Nevada-Las Vegas who crunches data to determine the nation's center. "It's a pacesetting region that is dominant in population growth, but also as a swing point in American politics."

The last time the U.S. center fell outside the Midwest was 1850, in the eastern territory now known as West Virginia. Its later move to the Midwest bolstered the region as the nation's cultural heartland in the 20th century, central to U.S. farming and Rust Belt manufacturing sites.

In the 1960s, "Will it play in Peoria?" was a common phrase that coincided with the U.S. center's location in Illinois. It was a measure of whether a politician or product could appeal to mainstream Americans with traits associated with Midwesterners, such as stability and caution.

But over the last decade, the Phoenix suburb of Peoria, Ariz., soared past its namesake Peoria, Ill., in population. With Arizona on track to surpass Ohio in electoral votes by midcentury, issues important to the West will gain in political sway.

The Census Bureau calculates the mean U.S. center every 10 years based on its national head count. The center represents the middle point of the nation's population distribution - the geographic point at which the country would balance if each of its 308.7 million residents weighed the same.

The latest 2010 figures show a loss of House seats for states including Missouri and those east of it, primarily in the Midwest's declining Rust Belt.

Eight of the 12 pickups in House seats occur in states west of Missouri, with Florida, Georgia, and South Carolina being the exceptions.

The fastest U.S. growth is occurring in the mountain West: Arizona, Colorado, Idaho, Montana, Nevada, New Mexico, Utah, and Wyoming.

As California's growth slows, many mountain state arrivals are Hispanic immigrants. Latino population grew a whopping 28 percent over the decade, while Asian numbers grew 31 percent.

Among other findings:

In Arizona, which gains a House seat, Hispanics accounted for roughly half the state's population increase since 2000, according to census estimates.

The western United States grew 13.8 percent from 2000 to 71.9 million people, surpassing the Midwest as the second-most-populous region. The Midwest rose 3.9 percent, the Northeast gained 3.2 percent.