There is a place in NE Iowa that offers hog hunts for sale, it is a fenced operation, although I think it is like 300 acres. I am not interested in starting a fenced/free range free for all here, but I will say that if the area is that large IMO you would by no means be shooting fish in a barrel.
Years ago I went on a hog hunt in Texas that I suppose was technically a fenced operation, but the property was large enough that the fence wasn't a factor and the hogs were plenty wild. I suspect that the place in NE Iowa would be similar.
Other than that, I don't know of any area in Iowa where you will find any wild hogs. If some exist, people get on them real quick to stop them from spreading.