The Daily Mail in the UK came out with this map showing the pattern of the most frequently cited ethnicity (or the mode in statistical lingo, in political lingo it is called a plurality if not a majority) in each county and State from the 2000 Census. Overall German ancestry (colored light blue) is most often cited by respondents followed by African Americans. 20 million (mostly in the Appalachian southeast) say American because they do not know their ancestry.
In Pennsylvania, where I am from, German is the most common ancestry in all but three of the 67 counties. The Amish speak a German dialect. Of course 13 years later the map could look very different with Latino Americans making a larger portion of the population. I know the map is hard to read I made it as bid as I could. Surprisingly, Mississippi has all but a few counties colored purple for African Americans being the most stated ethnicity while it is a state that voted solidly against Obama twice. The Caucasian population must live in more populated areas. Connecticut, where I lived for two years, has a large Italian population
Colin Woodard of Tufts University produced a county level map with 11 different political regions which seems to have some correlation to the ethnic map at the top such as many (but not all) of the counties of Greater Appalachia describing themselves as American. He uses his model to explain the failure of the Obama Administration and the families of the Newtown, CT victims to pass an assault weapons ban that Sens. Pat Toomey R-PA and Joe Manchin D-WV proposed. Manchin of West Virginia represents a state in the Greater Appalachia region. Southwestern PA, where I grew up, is also included in Appalachia though it is ethnically different from the rest of the region. The central part of the state that Toomey represents, while ethically similar, is placed in the Midlands region (Pittsburgh where I live now is right on the border with Appalachia and is sometimes called the Paris of Appalachia) while the upper row of counties is placed in the Yankee region. According to Woodard Manchin took a bigger risk making the deal than Toomey.
I had a big response to this post. Yet another map has been produced politically classifying the 3,100 counties into 15 categories which are described in the Washington Post. This map is interactive. If you move your arrow key over each county you can see how its classified. Below the interactive version is embedded. Is there more correlation with the map at the top than there is with the second map?