I wasn't able to find the actual marriage licence online, however I did find it listed online in the Illinois State State Archives. The information is as follows:
Groom: ELY, CHARLES L
Bride: COOPER, SARAH S
Date Volume: 1891-06-04
Page: 00E 0341
Lic No.: 091M0908
According to the archives site, you can get a copy of the actual license from Illinois Regional Archives Depository (IRAD) at Norther Illinois University (NIU). If you call them first and give them the info above, they should be able to tell you if they have a copy. If they do, they will send it to you for a very small fee. Here is their contact info:
Northern Illinois University (NIU)
Illinois Regional Archives Depository
c/o Regional History Center
Founders Memorial Library, Rm. 400
Northern Illinois University
DeKalb, IL 60115
Hours: Mon.-Fri., 8 a.m.-12:00 p.m.; 1-4:30 p.m. (except state holidays)
I have worked with them before and they were very helpful and got my copies fairly quick.
Hope this helps!