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.
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.