The michigan is known as mitten state.
What are mittens?
Gloves which cover the entire hand but do not have separate finger openings or sheaths are called mittens.\nYou can read more about it here
Why is michigan called a mitten state?
Because if you see the map of michigan, its lower part shape closely resembles to that of a mitten. Heck, there is even a poem which says michigan is mitten.
Though much on her physical form has been written,
You will note the lower part is like a mitten,
And when around her shores you come.
Please note the cities near her thumb.
You can read more about the poem here