The state of Illinois offers several databases that can be a significant help in your research. Since 1985, the Illinois State Genealogical Society (ISGS) has cooperated with the Illinois State Archives to create an index to Illinois marriages occurring prior to 1901.
My mother wanted to stay active in her retirement but was physically limited, so she spent her mornings transcribing the Kankakee county married records from oversized photocopies of the original books into a software application used to index the records. The database can be searched at http://www.cyberdriveillinois.com/departments/archives/marriage.html
French Canadian settlers came to Kankakee County in 1834, after the federal government signed the Treaty of Camp Tippecanoe in 1832. The earliest marriage records for Kankakee are filled with surnames like Lambert, Brunnenier, LaMuret, and Jeannot. Over time, there was a decline in French surnames and an increase in Irish and German.
While the online Illinois marriages database provides only the names, date, location, and file numbers for a marriage, the original Kankakee books usually included residence, occupation, parents, and witnesses. Mom and I were fascinating by number of men living in Chicago who married wives in Kankakee county. Keeping in mind that many of these records are pre-1871, the Kankakee marriage records are a valuable resource to check if your ancestor was married before the Chicago Fire.
So take another look at the Illinois marriage database. Be VERY creative with surname spelling and you may track down your illusive pre-Fire ancestors.