Wikipea has an interesting map of US ancestries by county: http://en.wikipedia.org/wiki/File:Census-2000-Data-Top-US-Ancestries-by-County.svg. German ancestry predominates in the North, and "American" and black predominate in the South. I find that I've lived in two black counties, two Hispanic counties, three German counties, one English county, one Italian county, and two Irish counties.
Interesting map. I grew up in a central Illinois town with a huge German-descended community who arrived in the 1840s when the area was being settled. Another large community was white southerners who came up during the Depression for industrial jobs in the area. The joke (which they tell) is that they were on their way to Chicago but their cars broke down. My family was Italians who came to work the coal mines in the 1910s and lived in company houses on the hill outside of town, next to the mines.
