Illinois sporadically recorded deaths prior to 1916. None of them are in the Illinois Pre-1916 Death Index.
Aaron and Sarah died before the 1870 Census.
1880 Scottville, Macoupin, IL
Willis Turner, b. TN, 60, farmer
Elizabeth, b. KY, 56
They didn't appear on the 1900 Census and therefore died before 1900.
I'd contact the Macoupin County Genealogical Society, www.macoupinctygenealogy.org/mcgs/#referencematerials
and ask if they have a local death index, indexed newspaper death notices and cemetery inventories. Successful Searching!