Michigan Railroad Map from MDOT
I stumbled across this while I was putting in the CR railway that runs from Utica to Detroit. It's a map of the main rail lines in Michigan (primarily those owned by the big four - CN, CSX, NS, and CR). I'm sure with a little more digging we could probably find further information on those "other railroads."
Railroads Operating in Michigan Map from Rail and Public Transit page on MDOT
Railroads Operating in Michigan Map from Rail and Public Transit page on MDOT
Re: Michigan Railroad Map from MDOT