I have access to Will County marriages beginning in April 1836, and ending November 1928. The records are in loose chronological order, according to when they were returned to be filed. In some cases an entire month, or part of the following month, must be searched to located the desired certificate.
Marriage dates can be obtained, for the years 1836 through 1900, by searching the state archives website. Please provide me with the entry from the Illinois Statewide Marriage Index, 1763-1900 that you are interested in.