This may be the plot at the Evergreen cemetery, Fort Atkinson, Wisconsin for my great great great grandparents, Hannah (Birge) and Dudley Cass.
Hannah was born October 11, 1826 to Abigail and Peter Birge in Monroe Center, Ashtabula county, Ohio. Dudley was born August 3, 1823 to Mary (Lyford) and Abraham Cass in either New Hampshire or Vermont or a third possibility, Quebec Province in Canada.
Hannah and Dudley were married October 14, 1847 in Conneaut, Ashtabula county, Ohio.
Hannah passed away May 27, 1899 in Fort Atkinson, Jefferson county, Wisconsin. Dudley passed away June 3, 1905 also in Fort Atkinson.
I'm not sure why a marker or headstone wasn't located as the Dodge Jefferson Genealogy website had listed both Hannah and Dudley.