Nearly one in seven Americans lives in the metropolitan areas of the country's three largest cities: New York, Los Angeles and Chicago. That's a startling stat that's hard to appreciate even after pondering maps of U.S. population density like this one:

Add metro Dallas-Fort Worth, Houston, Philadelphia, Washington, Miami, Atlanta and Boston to that group (totaling the country's 10 most populous metros), and nearly one in three Americans lives in these few spots on the U.S. map.

"We are a much more big urban nation than a lot of people think," says William Frey, a demographer with the Brookings Institution.



New Census data released Thursday further suggests that within the last year (from July 1, 2012, to July 1, 2013), virtually all of the country's population growth took place in metropolitan areas, with a significant chunk of it even further clustered in and around the largest cities. Over that year, the number of people living in metropolitan America increased by 2.3 million, a figure that reflects both natural growth and in-migration. The population in what the Census calls "micropolitan statistical areas" – smaller population centers with a core of fewer than 50,000 people – grew by a mere 8,000 souls.

As for the rest of the mostly rural country, the population there dropped between 2012 and 2013 by 35,000 people.

Those areas are neither attracting new residents nor producing many of their own, a sign of the exodus of young adults who might be having their own children now. "After decades and decades of out-migration of relatively young people," Frey says of non-metro America, "what you have is a population that’s much older."

By contrast, looking at the sheer numbers, these are the places that grew the most in the last year:



Census Bureau

About one-third of the country's population growth last year was in these 10 large metros, which grew much faster than smaller metropolitan areas. Frey has divided historic data on population growth looking at metros larger and smaller than 500,000 people, going back more than decade. Not that long ago, smaller metros were growing faster than the larger ones:



The Y axis shows net growth per 100 people. (Courtesy William Frey)

Among all metropolitan areas, Frey has broken down population growth over the last decade even further here:



(Courtesy William Frey)

It's a little soon in a still-weak economy to draw sweeping conclusions from these last two charts about the relative appeal of inner cities compared to exurbs, or about even broader geographic migration trends at a time when housing mobility is at a historic low. But, as the Census points out, America is still slowly, steadily, growing more metropolitan than ever.

Those 2.3 million new people living in metropolitan America now? Their arrival means the share of the U.S. population living in and around these urban places has inched up from 85.3 percent in 2012 to 85.4 percent.