Pellston, The icebox of the nation!.
If you are hitting Pellston on the way up, Drive to Indy, Take 31N out of Indy.
At South Bend you can take 20 east towards Middlebury to hit 13 N which turns into 131 N in Michigan or stay N to I94 E which will take you to Kalamazoo and 131 N.
31 N is a nice drive once you get off the loop in Indy. I live near Kalamazoo and given the choice would always take 20 across to Middlebury because I like 2 lanes over 4. I have driven over 2 million miles and like the scenic route when possible. Yes it is slower to go to Middlebury. Watch out for the Amish Buggy's.
Once you get to your site, you stated Mill Creek. We did a day trip to Historic Mill Creek State Park a few years ago. It was great if you like historical sites. The recreated sawmill was awesome, there is the opportunity to zip line and a nice swing bridge if you are so inclined. My son loved it. Also lots of hiking trails.
Colonial Michilimackinac State Park is right under the south end of the Mackinaw Bridge. A great historic site with lots to see if you like historic themes. They do digs on site and you can talk with the people and they will show you what they have found. The view is also great.
A few miles west in Cheboygan there is a nice microbrewery that has a great Blood Orange if you like breweries. The Rusted Spoke brewery in Mackinaw looks over the Lake Huron, beers are okay, the view is good from the second story. It is a nice break from the tourist boulevard.
If you can't tell I like history and beer.