The fastest growing area in the United States between 2000 and 2010 were exurbs:

Between 2000 and 2010, the total U.S. population grew about 10 percent, from 281 million to 309 million. Over that same time, the exurban population grew by more than 60 percent, from about 16 million to almost 26 million people, according to the analysis. As this chart shows, rates of growth are significantly higher in exurban areas than in more urban or densely populated areas.

A new interactive map from the Urban Institute shows how the growth rates in exurban areas have been higher – and in some cases much higher – than the growth rates in their corresponding metropolitan areas. The map is based on an analysis by U.S. Census Bureau researchers Todd Gardner and Matthew Marlay, who looked at census data from 2000 and 2010, and American Community Survey data from 2005 through 2009. Their data is also available in a sortable table.

The exurbs of Las Vegas, for example, saw an average annual growth rate of 17.2 percent between 2000 and 2010, while the metropolitan area as a whole had an average growth rate of just 3.6 percent. Phoenix’s exurban growth rate was 14.7 percent during that time, compared to its metro-wide rate of 2.6 percent. Omaha’s exurban rate of 11.9 percent also outpaced its metro-wide rate of 1.2 percent. Ninety-six of the 98 most populous metropolitan areas saw higher growth rates in the exurbs than in the metro areas as a whole between 2000 and 2010…

But it wasn’t all just pre-crash exurban booming. Some metro areas continued to see their exurban populations grow between 2007 and 2010, after the crash and through the recession. From 2007 to 2010, metropolitan areas grew about 2.4 percent, while exurban areas grew by 13 percent. Some exurbs even out-performed their pre-recession selves. “In 22 of the largest 100 metros, the average annual growth rate in the exurbs from 2007 to 2010 was higher than that of the previous seven years,” the researchers write.

As you might expect, the majority of the fastest growing exurban areas were in the South and West.

By definition, the exurbs are on the metropolitan fringe. However, once they reach a certain population or development moves past them, they are no longer really the exurbs as further out communities then take up the label. How long does the “average” exurb last before it simply becomes a suburb? I suspect this might differ city by city as they expand at different rates. For example, the cities of the Northeast and Midwest have a longer history and much of their explosive growth has already concluded.