The closest one that I know of to you is Mother's Reef which is in or near Battle Creek. Very nice people with a nice selction of corals and small frags.
A little farther north, on the south side of Hastings, there is Aquatic Expressions (I think that is what it is called). They have a website and an ad in the Grand Rapids yellow pages. Very cool store. It is owned and operated by 2 guys. They do mostly set-ups and maint. during the week, so the showroom is only open on Saturdays. I would definitely check them out.
If you are venturing any farther north, there is Eco Reef in Zeeland, VI Pets in grand rapids (this is my personal favorite--go to the Plainfield location, much better than the S. Division location), Chow Hound on 28th St. in GR has a nice selection - talk to Mark there, he knows his stuff, and Solomon's Seas in Grandville.
If you are looking to attend a decent frag swap, check out
www.grmas.(com or org, don't remember which. I am a member of this club and we are having a frag swap on sat. March 3rd. It should be really good. Another place with a lot of good info is on
www.michiganreefers.com. Its all Michigan, so there will be more locals on that board. There is also a lot more info on the GRMAS swap and others.
Hope that helps.