My guess is that there was no 'listing' that still exists. I believe that the 'Donner Party' started out there though, and reading some on it might give info if there are other lists.
Springfield is in Sangamon County. This is a link that will have info on many things for the county, but you might search more places on the internet also. http://www.rootsweb.com/~ilsangam/sangamon.htmhttp://www.rootsweb.com/~ilsangam/sangamon.htm
Have you tried finding the obituary or the death certificate for your grandmother? Maybe someone gave info that was used on those. Did Grandfather ever mention where he might have met her? That might help find out where she was living and you could search there for a marriage. You might have luck with the other questions on the family by looking at old census records. They will list a birth state, age, etc. Sometimes the wrong info was given so it is good to compare a couple of them.