Census Atlas of the United States. This is my salute to the rugged individualist. The Census form asks people to identify their ancestry and most people meekly admit to being Swedish, or Native-American, or Italian-English-Irish, etc.
But there will always be somebody who sets his/her jaw, folds his/her arms and says "I'm an American!" This table shows the percentage of people in each county who identified their ancestry as "United States, a state name, Southerner, American or Northern American." The darker the color, the higher the percentage. The darkest represents about 7% of the respondents.