WASHINGTON – After two centuries of boom and bust, America’s population growth may finally be leveling off.

In all, the U.S. population is now increasing a bit faster, thanks to an improving economy, but not enough to lift growth above its lowest level since the Great Depression.

The nation is getting older and is less likely than before to be married, with women waiting longer to have children, if at all. Immigration from other countries is on an upswing after years of sharp declines during the recession but may never return to the peak level it reached in the early 2000s.

New 2012 estimates released Thursday by the Census Bureau offer the latest snapshot of the U.S. population, showing signs of revival and change in pockets of the U.S., especially in Sun Belt states hard hit in the recession.

“After decades of wars, a depression, immigration surges, baby booms, boomlets and busts, we are entering a new era of modest growth,” said William H. Frey, a demographer at Brookings Institution who analyzed the numbers. “This is a result of our aging population, lower fertility rates and immigration levels that will probably not produce sharp population spikes.”

As a whole, the U.S. population grew by 2.3 million, reaching 313.9 million people. That growth rate of 0.75 percent only slightly outpaced the 0.73 percent rate in 2011.