Hopefully, you are still looking in this forum for information about your Damm lineage. I have additional information.
My Grandfather was Dieter DAUM, son of Dieter DAMM. He had a brother named Elias Damm (I think this is your Elias).
I have a copy of the 1880 Census for Greene County, Illinois for the household of Dieter Damm. At that time, the following were in his household:
Damm, Dieter - age 28 - b. IL Parents born in Darmstadt, Germany.
Elizabeth - wife - age 26 - b. IL parents born in Bavaria Her full name was Anna Elizabeth Meister.
Elizabeth - daughter - age 9 - b. IL
Dieter (my grandfather) - age 7 - b. IL
Bena - daughter - age 4 - b. IL
Catharine - daughter - age 3 - b. IL
Elias - son (your grandfather?) - age 1 - b. IL.
Bena Damm - mother - age 60 - widow - born Darmstadt, Germany.
Rathgeber, Catharine - sister - age 32 - widow - b. IL
Rathgeber, Dieter - nephew - age 13 - b. IL
Rathgeber, Frederick - nephew - age 11 - b. IL.
Catharine's husband was born in Darmstadt, Germany - don't know when or where he died.
Verbal family history indicates that Dieter Damm's children began to change the spelling of the surname to DAUM. This happened around the turn of the century (1900). I have a photograph of Dieter and Anna with some of their family. Dieter and Anna appear to be elderly.
I remember Aunt Kate (Catharine) and Aunt Bena. When I was a small child, we would go visit them whenever we made a trip to see my grandparents in Jerseyville, IL. Additional notes I have on the Dieter Damm family is that he was a farmer until he retired to Greenfield, and later on to Carrollton, IL.
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I hope to hear from you soon.