I've actually found most of the growth is in rural communities, not large urban areas. In the 2010 census, you saw low increases, or even decreases in these areas, while more rural areas gained large numbers.

For instance, Cook County in Illinois (where Chicago is located) saw a 3% drop in its population from 2000-2010. By contrast, Cass County in North Dakota (where Fargo is located) saw a 21% population increase from 2000-2010.

(source was 2010 census - http://www.usatoday.com/news/census/index?refresh=1)