As Lapsody pointed out, there has been a general migration towards cities since the Depression. Lots of factors there, also. The jobs generally pay better, and there are more of them. And if you have a more formal education, you have a lot of opportunities in that environment. Farmers and rural area folks may be intelligent, and some of them even well-educated. But for a variety of reasons (including the annual "Farm Bill" I posted about a week or two ago), it's difficult to make a living as a farmer. And we need fewer of them as machines enable efficient factory farms that require fewer people to staff. That's also affecting manufacturing jobs (plus off-shoring). A good plumber can do very well, but we only need so many plumbers. The advantage they have is their job can't be automated or off-shored, though. Even among technical people, we're starting to see off-shoring of design and other "brain" jobs because if they have a computer and a connection, they can work from Romania (or wherever), and corporations can pay them less.

As I said up-thread, it's a complex array of factors affecting who's moving where, and the reasons they are moving, and the opportunities available to those folks. Formal education tends towards cities, tends to better paying jobs**, tends towards broader exposure to new ideas and people***, etc. That's why you can have a solid blue city in a red state. Tucson is very blue, and Phoenix is light blue. The rest of the state (rural) is red.

**I wish I earned as much as a crane operator that never went to college. Those guys make a fortune, there aren't very many of them, and the work is very demanding (which is why they're well-paid).

***Via college and grad school, I was exposed to people from all over the world (especially during my time in the dorm), as well as different regions of this country. Exposure to ideas I didn't even know existed. I wouldn't have had that if I grew up on a farm outside of Topeka.