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 during the recent 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 was higher than the 0.73 percent rate in 2011, ending five years of slowing growth rates. Nevertheless, the rate of growth remains stuck at historically low levels not seen since 1937, restrained by reduced childbirths.

Over the last year, the economy has shown improvement, with the unemployment rate declining modestly and U.S. migration edging up after hitting a record low in 2011. As a result, states including Texas, North Dakota, Colorado, Oregon and Virginia posted population growth increases as many young adults moved out from their parents’ homes, seeking to test the job market in areas with thriving economies in energy or technology.

Still, the nation continues to get older, due to aging baby boomers and fewer people in their child-bearing years. Newly released census projections now show that U.S. growth may have largely peaked, barring a significant and sustained increase in new immigrants. The numbers put U.S. growth in the next year or two at just under 0.8 percent, before flattening and gradually falling to rates of about half a percent, a level unseen in more than a century.

U.S. growth reached a high in 1950 of more than 2 percent, lifted by the post-World War II baby boom.

Immigration to the U.S. was on the uptick in 2012 after falling significantly during the downturn, although it remained far from the level seen during the mid-2000 housing boom. Congress is expected to debate an overhaul of immigration law next year.

“We will now need to cope with population challenges that past growth has left us — notably, the needs of a large aging baby boom population which will require resources for its medical care, and the social and economic integration of first- and second-generation immigrants,” Frey said.

The Census Bureau released state population estimates as of July 1, 2012. The data show annual changes through births, deaths, and domestic and foreign migration.

The data suggest that the impact of the recession on formerly fast-growing Sun Belt states may be waning. Nevada had more residents move into the state this year after suffering migration losses in previous years. Arizona and Florida, two other housing boom-and-bust states, also showed renewed migration gains after seeing their growth drop off sharply at the end of the last decade.

In all, 26 states grew faster this year compared to the previous year, of which 19 are in the South and West region.

“These gains remain far smaller than those each state experienced during the economic boom, but reflect considerable improvement over the situation at the depths of the recession,” said Kenneth Johnson, a sociologist and senior demographer at the University of New Hampshire, referring specifically to Arizona, Nevada and Florida.

In contrast, Massachusetts, New York and New Jersey saw more residents move away compared to the previous year.

North Dakota grew faster than any state in the nation, climbing by 2.2 percent from July 2011 to July of this year. The District of Columbia was next-fastest growing, followed by Texas, Wyoming and Utah.

Two states lost population: Rhode Island and Vermont.

Kimball Brace, president of Election Data Services, said if the 2010 census had been held this year, Minnesota would have lost a seat in the House of Representatives and North Carolina would have picked up one due to the shifting population figures. Based on continuing losses, Rhode Island is now on track to lose one of its two seats with just 33,000 people to spare — potentially to the gain of Oregon, which is about 59,000 people away from gaining a sixth seat.

California remained the most populous state, followed by Texas, New York, Florida and Illinois.