We have to drive through a lot of small towns and have often asked the same thing.
No, its not agriculture. Not prisons either.
Small businesses don't seem to last long. They'll open and before long, they've closed. Mostly because most of them choose a business that would likely fail in a big city!
The homes - some are very well kept, newish vehicles out front. Others are trashy, pick up trucks sitting up on blocks.
A woman I know owns a business in the next town over, her son came home after getting in trouble with the law. He lives in a crappy little trailer next to the house but his wife and their child live inside with the in laws. Supposedly, the son helps on their farm but it went under a few years back.
They signed up with Butterball who controls everything they do. They had to go even further into debt to build a turkey barn. Butterball pulls up every years and unloads a schlew of baby turkeys who they then fatten up for Thanksgiving. Butterball pulls up, loads up the fat turkeys and they get a check in the mail. Problem is, they pay out a lot more than Butterball pays them.
I got into a conversation with a woman behind the counter when I paid for gas. She said she lives several small towns away and commutes while her husband runs their farm that's actually broke.
Heck if I know how most of them survive.