Domm: From Germany-also Dohm/Dahm.......

Greetings:
My mother was Irma Mae Domm, b. 31 March 1916 in Seneca, IL, d. December 1998. She married Gerald F. Derry. Her fathers name was George Domm, who married a Irma Norton, no birth or death dates for either. Georges father was John Domm, who married Mary White, again - no dates.
I have seen various spellings for her maiden name: Domm/Dom/Dahm/Dohm
All that I know of her family (Domm's) is that they are from Germany.
If you can, please help! I've been at a deadend since my mothers passing 2 years ago.
ThankYou,
D. Doc Derry