In case it's helpful to your research, there are death notices published for Fredericke Griewahn Haberkorn in Milwaukee's German newspapers. There is also a John Griewahn (44 yrs, survived by Anna) in these papers who died in April 1888. These are the only Griewahn entries found in "Milwaukee's German Newspapers; an index of death notices and related items" (1844-1950). There are about 50 Haberkorn entries.
Gary Rebholz, compiler/editor
Indexing Milwaukee's German newspapers continuously since 2007... helping family researchers collect evidence of our historic German-American culture.