I can help you out...As a "side trip" from my own frustrating search for my grandfather's(William Howard Mohn) parents in Peoria, IL.
Several years ago I wrote to every Mohn surname in the Peoria phone book.From one respondent I received a detailed family history of Peoria-area Mohns prepared by one Edith Mohn.We could not tie my grandfather in, but it has a wealth of info going back to early 1700s in Germany that includes your ancestors.
Henry Mohn (b. Oct 1878, Illinois) married (1) Bessie Compson on 7 Jan 1903.He married (2) Annie Callear.He died 1917 and is buried in Pottstown Cemetery, Kickapoo Twp., Peoria County, IL.His children were listed as Earl Mohn (coincidentally, my father's name was Everett Earl Mohn!) and Margaret Mohn (m. ___ Finley).
Henry Mohn's parents were William Frederick Mohn (b. 14 May 1847, in Duchy of Nassau, Prussia/Germany; d. 3 Aug. 1934 in Limestone Township, Peoria, IL) and Margaret Ann Glenn (b. 1860; d. 1922.
There's much more, but my photocopied manuscript is losing its toner quickly -- the curse of that technology.I suspect the Peoria Historical Society could put you in touch with a good reproduction of this 50+ page history.
I found members of the extended Mohn family in Peoria quite friendly and willing to help me make connections, so I encourage you to contact the genealogy/history societies in that area.