Not sure if this is the one you're looking for, but the online Appleton Public Library Obituary Index lists Mathias N. DIEDRICH whose obituary was published in the Appleton Post Crescent on 13 April 1992. Instructions are posted on their site for ordering a copy of the obit.
Online results at findagrave.com show Mathias Nicholas DIEDRICH (20 January 1916 - 12 April 1992) at St. Mary's Cemetery at Hilbert (Calumet) County and his wife, Catherine M. CORDY (18 March 1918 - 12 April 2004). They were married 30 April 1936.
Although Mathias' obit is not transcribed at findagrave.com, Catherine's is. Names of their 10 children are also listed.