Trust me, farmers don't intentionally feed feral hogs. The best hunting is on private land, of course, at least around here. There is some good numbers of hogs on a local WMA, but you have to use buckshot (30 yards at best) and they tend to stick to heavy cover by day. I hunt my own land by night when the hogs come out. I've taken a few in daylight, danged few.
I hunted one place, 2 day hunt for 180 bucks (real reasonable) and shot my eatin' size hog limit the first day. The place was UNREAL overrun with hogs. Land owners are learning to turn a pest into cash, though. Good hog hunt will generally run 500 now days from what I've seen.
There's plenty of hog hunting on public land in east Texas. You'll need a 48 dollar annual public hunt permit to hunt and each WMA has its own rules. See the Texas Parks and Wildlife Department site for details.
I'll let other folks speak for their states. All I really know is Texas when it comes to hogs.