Johnson said the number of dying counties is rising not only because of fewer births but also increasing mortality as 70 million baby boomers born between 1946 and 1964 move into their older years. "I expect natural decrease to remain high in the future," he said.
Among the 20 fastest-growing large metropolitan areas last year, 16 grew faster than in 2011 and most of them are located in previously growing parts of the Sun Belt or Mountain West. Among the slowest growing or declining metropolitan areas, most are now doing worse than in 2011 and they are all located in the Northeast and Midwest.
New York ranks tops in new immigrants among large metro areas, but also ranks at the top for young residents moving away.
In contrast, the Texas metropolitan areas of Dallas, Houston and Austin continued to be big draws for young adults, ranking first, second and fourth among large metro areas in domestic migration due to diversified economies that include oil and gas production. Phoenix, Las Vegas and Orlando also saw gains.
By region, growth in the Northeast slowed last year to 0.3 percent, the lowest since 2007; in the Midwest, growth dipped to 0.25 percent, the lowest in at least a decade. In the South and West, growth rates ticked up to 1.1 percent and 1.04 percent, respectively.
"The brakes that were put on migration during the Great Recession appear to be easing up," said William H. Frey, a demographer at the Brookings Institution who analyzed the migration data. "Native migrants are becoming more 'footloose'-following the geographic ups and downs of the labor market-than are immigrants, who have tended to locate in established ethnic communities in big cities."
"Immigration levels are not where they were a decade ago, but their recent uptick demonstrates the important safety valve they can be for areas with stagnating populations," he said.
Mark Mather, an associate vice president at the Population Reference Bureau, noted that political efforts to downsize government and reduce federal spending could also have a significant impact on future population winners and losers.
Since 2010, many of the fastest-growing U.S. metro areas have also been those that historically received a lot of federal dollars, including Fort Stewart, Ga., Jacksonville, N.C., Crestview, Fla., and Charleston-North Charleston, S.C., all home to military bases. Per-capita federal spending rose from about $5,300 among the fastest-growing metros from 2000 to 2010, to about $8,200 among the fastest-growing metros from 2011 to 2012.
"Federal funding has helped many cities weather the decline in private sector jobs," Mather said.
The census estimates are based on local records of births and deaths, Internal Revenue Service records of people moving within the United States and census statistics on immigrants.
Business Editor Jared Hunt contributed to this report.