If you are flying into Michigan for the wedding, there are a few options as to airports.
I would recommend South Bend, IN. It seems to be the closest. It's about a 50 min drive northwest to Pottawatamie from there. Hopefully we'll be able to arrange some car pooling to make that easier.
There is also Kalamazoo, MI. That's north of the resort, but also about a 50 min drive.
Another option people are looking into is flying to Chicago's Midway and driving up. It's 112 miles. So about two hours. Just make sure you leave plenty of time. Chicago traffic can be brutal.
Check and see what airport works best for you.