17.9 million people
These 154 counties are scattered around the country and are generally located near large colleges and universities. Filled with college students, about 8% of the population sits between the ages of 18 and 21 – far higher than any other type. These counties also hold a large number of college graduates, 34% of their population has at least a bachelor’s degree, and they are less diverse than the nation as a whole, about 85% white, 7% black and 7% Hispanic. President Barack Obama won the vote coming out these counties in 2012 by bout four points, 51% to 47%.