Those estimates show more Americans are moving from Rust Belt and Northeastern cities, including some of the largest metropolitan areas in the country, in favor of booming cities and suburbs across the Sun Belt and the West Coast.

"The economy has gotten better. People are not hunkering down anymore, especially young millennials who were put in a vice in the beginning of this decade," said William Frey, a demographer at the Brookings Institution.

And after years of decline, rural America is starting to reap the benefits of a more mobile population. The number of Americans who live in nonmetropolitan, or rural, areas grew by about 37,000 residents in the last year — a relatively small increase, but one that represents a sea change from years just after the recession when so many people moved out of rural communities in favor of larger cities.