text: what is the largest county in size in the state of michigan?   county information for michigan   there are 83 counties in the state of michigan.  the largest michigan county by size (land only) is marquette county, which is 1,821 square miles. if you take into account water as part of the county, which some statistics do, keweenah county takes the lead with 5,922 square miles compared to marquette county at 3,425 square miles.