The St Joseph in Northern Indiana is an excellent Steelhead fishery!
They have a website; www.rippleguideservice.com
though it isn't working at the moment. Maybe they are updating. Try it later. It flows into Southbend IN, gets a huge steelhead run. You will need at least a 6 wt though, I would say with a 150 yards of backing. An 8 wt with at least 150 yards of backing would be preferable. From what I know the St. Joe is hard to wade (nearly impossible) The Dowagiac is a trib and wadeable I think. It is in Southern Michigan.
Dustan Harley owns Ripple Guides, he is very knowledgeable. Shoot him an email if you cant get the site to come up later.
Also the Muskegon is another option though 3 hours further. I have fished it a couple of times and had a ball with the kings. You may want to try them first, they are more of a sure thing. They aren't as fast as a steelhead, but incredibly powerful, they leap and they run. I have several times seen the bottom of the spool on 230 yards of backing (while the drag was tight enough to pluck!) They are a hoot!
These are pictures from our first trip to the Muskegon. The guides question about fishing was; "Do you want to fish for Steelhead or do you want to catch Kings?" Kings in October a fun trip!