Answers come from comparing the Census Bureau's just-released estimates of metropolitan area populations in July 2012 with the results of the Census conducted in 2010.
The focus here is on the 51 metro areas with populations of more than 1 million where 55 percent of Americans live, most of them of course not in central cities but in suburbs and exurbs.
Two growth champs stick out -- Austin and Raleigh. A half-century ago, neither of them amounted to much.
The counties now in metro Austin had 300,000 people in 1960. Those in metro Raleigh had 260,000. Now metro Austin is 1,834,000, and metro Raleigh is 1,188,000.
Austin's population grew by 6.9 percent and Raleigh's by 5.1 in 2010-12. That's huge growth in just two years.
Both are high-tech centers with major universities. They had the biggest rate of domestic in-migration of any million-plus metro areas in 2010-2012.
They both have reputations as cool cities. More important, they both have creative and vibrant private sector economies, fostered by relatively low tax rates and sensible regulation.
Raleigh's taxes and cost of living compare favorably with those in most states in the Northeast. Austin is attracting a lot of people from California, where the top income tax rate is now 13.3 percent. Texas's income tax rate is zero.
Next on the growth list are Texas's three other million-plus metros, Dallas, Houston and San Antonio, which grew by 4.3 percent in 2010-12.
Their populations increased by 622,000 people. That's 12 percent of the entire nation's population gain during that period.
It's more than metro New York, Philadelphia, Boston, Baltimore, Hartford and Providence combined. Texas is making a huge contribution to the nation's demographic and economic growth.
Not far behind are Orlando, Fla., with its tourism industry; Denver in healthy Colorado (the nation's lowest obesity rates); Metro Washington, D.C., which has the advantage of federal tax dollars pouring in; Metro Miami, where growth is greatest in farther-north Broward and Palm Beach counties; Charlotte, N.C., the nation's No. 2 banking center; Oklahoma City (natural gas); Phoenix, Ariz. (though immigration is way down); Nashville, Tenn. (health care and music); Salt Lake City (high birth rates); Seattle (high-tech, despite the rain); and Atlanta.
Lagging somewhat is California. The combined Los Angeles-Riverside metro area is growing just slightly above the national average. More people have been migrating from California to other states than moving in from other states since 1990, and immigration there is sharply down.