the midwest guys can probably help you more than I and I hope some reply. I usually look for any higher areas in fields (because obviously you want rain water to flow away from the house foundation and not into it ) . a clump of trees in a field is a good indicator to an abandon site , over the years the farmers didn't want to do any damage to machinery and avoided the area and the actual foundation over grew with trees and brush. sometimes just a really large overgrown tree or two by a road can indicate a dwelling was present at one time. once your in a field things to looks for are red brick pieces , glass , pottery or china chips , these are usually only present where a house once stood.