Officially Illinois didn't use death certificates until 1916. However my source says Knox County Clerk had some birth & death records as earlyas 1877. I'd contact them.
The death records at the Illinois Repository Archived Documents, has deaths 1877-1935. They also have marriage records 1830-1943.
The Knox County Illinois Genealogy & History group, http://knox.illinoisgenweb.org/home/kcgs.htm
will do research and I'd ask them if they can look for Emma's newspaper death notice and if they have inventoried cemetery records.
I also didn't find Joel's second marriage record. They may have his obituary too. Successful Searching!