Not sure if you already have this, but there is a marriage record in Kent county MI 9/16/1887 of Nathan Jacob Hamburger 50 from Germany to Lucy Ann McSherry Defanan 43 from Canada.witnesses were Mrs. Helen Philips of Grand Rapids and Laurence Curran also of GR.As you said, this couple is in Kent county MI 1880, showing William 13 WI, Minnie 11 IA, Francis 8 MI, Nathan 3 MI, Ester 1 MI.
In 1870 I find in Clayton county IA Lucy Ann Defus (Defno?)25 Canada, William 5 WI, Mary 2 IA.
In same county in IA on a death index 1880-1887 is a Caroline Deffinan, which spelling is close to the one on the MI marriage for Lucy.
I looked at the adjoining county in WI, Grant county, but could find no marriage or birth records.
There are 2 Oak Ridge cemeteries in MI that are possible, one in Berrien county MI, and one in Bay county which is near Saginaw.But I had no luck finding their burials.