1870 Petersburg, menard, IL
Chas E. Elliott, b. OH, 34, physician
Mary, wife, b. OH, 32
Chas E., b. OH, 10
Elizabeth Earl, b. OH, 18
C. E. Elliott, b. OH, 45, physician
Mary A., b. OH, 41
Charles, b. OH, 20, school teacher
Mrs. Charles Elliott
Died: oct 1844
Buried: Forest Hill Cemetery, Piqua, Miami, OH
I think this is Mary because they had previously lived in Miami Co. OH. Although she isn't listed in the Illinois Pre-1916 Death Index.
You can contact the Menard County Historical Society & Museum, www.museumsusa.org/museums/info/1165964
and ask if they'll copy her death notice. They might have other info about her death.
In 1900 Charles senior was living with his son and family in Wellington, Sumner KS and listed as a widower. Successful Searching!