Over the past year, the core counties of major metropolitan areas lost 67,000 domestic migrants (people move between a metropolitan area and somewhere else in the nation). Suburban counties gained approximately 72,000 domestic migrants, while exurban counties gained 49,000 domestic migrants (Figure 2). Because of their lower population base, exurban counties had the highest relative rate of net domestic migration, at 0.34% of their 2010 population. This is more than three times the rate of the suburban counties (0.11%) and far higher than the minus 0.09% of the core counties (Figure 3).
http://www.newgeography.com/content/002766-still-moving-suburbs-and-exurbs-the-2011-census-estimates