Listed below are six coordinates. There is no reason to actually go to any of the coordinates. When the puzzle/hunt is solved you will have a good idea of where you actually need to go.
1) N 42 16.259 W 87 54.743
2) N 42 16.559 W 87 49.233
3) N 42 20.645 W 87 51.592
4) N 42 23.846 W 87 50.078
5) N 42 24.704 W 87 55.021
6) N 42 19.942 W 87 53.212
7) N 42 xx.xxx W 87 xx.xxx
This isn't necessarily mathematical. Find how the six relate, and this will lead you to the seventh.
The solution will put you at the entrance to a Northern Illinois park. Once you figure out the park, go there. Near the sign for the main entrance to the park you will find a large green box (about 80 feet away) with some numbers written on it. Copy down the six digit number on the west side and the six digit number on the left of the south side (preceded by a "D"). These numbers will become the basis for the location of the final cache.
Calling the west digits ABCDEF and the south digits UVWXYZ plug the results into the following final cache location:
N 42 (W-E)(X-B).(Y-C)(U+V)(F+F)
W087 (D+F)(U+E).(A-D)(X-V)(Y+U)
The cache itself is an ammo can placed within a mile or so of the green box. It is relatively near a path although the proper approach may not be obvious. All locations involved close at dark.
I won't be offering any hints initially. After a few finds I plan on easing up some and may give away a hint or two. ;)
OK, now that a few more have solved it I've added the third hint.
Happy Hunting!!!