I can understand why they were married in Bay City then. There weren't roads going up to Harrisville from the Saginaw valley at the time. So they were going to be travelling by boat up the shore. There was a regular route that went Bay City - Standish - Tawas - Harrisville - Petoskey - Mackinac. The ships weren't able to make it upstream to Saginaw (the river was too shallow and clogged with lumber coming downstream). So the ships docked at the mouth of the bay. There were boarding houses in the area and it's possible this was the last minister they were going to see before moving up there. And no woman would have gone north with a man with whom she wasn't married. He probably spent time building the house for her, then came back to get her and they got married at the port city, rather than travelling a couple of days back and forth to Saginaw.