The Illinois regional centers have been helpful to me in the past, but they may not have everything.
I'd suggest looking for the county website for Peoria, and see what it tells you about marriage records specific to them.
I recently got a 1905 marriage record from Macoupin County, Illinois, and it appeared the only way to get this one was directly through them. I didn't have an exact date, but I did have a newspaper item of 3 lines that gave me a location. (The couple had apparently eloped from a few counties away.)
The record I got was well worth the $5 fee. It had everything I was looking for, including confirmation of both parents' names. And it is an image, not a transcript.
Hope this helps!