I live in Canada so I regretfully cannot help you much,
(although I do have one suggestion!)
but I wish you luck. I just started my 2 years of private cegep/college that are needed before university, and I was really worried I made the wrong decision and wouldn't like it. That my dad would end up wasting his money paying for the private one, and that I would have been happier at the public (and almost free cegep). Today was my second day and I actually love it. I cannot imagine myself anywhere else! I'm so happy I decided to stick with my initial decision and grateful my dad accepted to pay for it in the first place.
So whatever you decide, just remind yourself that it might be hard at first, but won't be as bad as you think, and that you will probably greatly enjoy yourself once you settle in.
I know anxiety attacks don't listen to reason
, but I just wanted to tell you this in case it could be of some encouragement.
So the college that comes to my mind is Champlain college in Burlington. It's a bit far... actually quite far from Iowa, but it seems to be exactly what you want. When I was driving through Burlington with my family, I couldn't help but feel that it was a great place (I want to find a way to study there for a semester). It's in the mountains so everywhere you go there is a nice view, and while the town isn't absolutely tiny, it isn't huge either. It's would be a perfect transition from boonie ville.
When driving through (we also stopped in town and ate), I noticed that around the core center of the town, it was all campus. I had the impression that Burlington almost was... a big campus.
Anyhow, I come from a big city and liked it because it was small, quaint and quiet, without being a hole in the middle of nowhere. The bonus is that they also have an equestrian club for people who know (or don't know) how to ride. I'm not sure, but you probably could keep your horse at the stable.
Whatever you choose, I hope it's everything you want, need and wish for. :)