This site contains about 138,000 waymarks worldwide. You can sort them and find lists of state historical markers. Most states in the upper midwest are included.
http://www.waymarking.com/cat/search...ical%20markers
The markers in the above site have good coordinates and usually have a picture. However, this is not a complete list of markers. You need to search your state historical society (or other agency that manages the markers) to find a complete list.
The historical society list may only have a marker name and a brief location description. You will have to estimate the waypoint until a firm coordinate can be obtained.
There are other sites on the web that list the markers but there is probably not a complete list on the web as things change. I think I was short about 75 markers that were not posted to the web.
Also, there may be a book published about the markers in your state. There was one in WI that I located through the state historical society.
PM if you are interested in taking on a project for your state and have questions about my experience.
Edit: Wow, I just looked at Michigan and see about 1,300 markers listed.