There are public records that will show you who owns the property. For Fond du Lac county, those records are found most easily through the Fond du Lac GIS here: http://gisweb.fdlco.wi.gov/gis_website/default.aspx . You would have to find out how to contact the owner of the property and go from there.
I often will do that leg work for prospective buyers or investors if they know the property that they would like to purchase and target. If it is a Bank Owned, Pre-Forclosure, or short sale then you will want to work with a Realtor that has dealt with those before as there are many hurdles to navigate through with those sales. I those types of properties among others.