The primary thing you need to know if planning a wedding in Illinois is that the license required is the one for the county where thewedding will take place.
Where you live does not matter, and I have had several couples who had to redo their vows and make them legal -- after driving across a county line to get into the county which issued the license.
If you are unsure of which county you wedding venue is in, be sure to ask. Check a map or call a county office if necessary. Then get a license for that county. If you are planning an outdoor wedding, check to be sure that your "bad weather backup location" (often, but not always, the reception location) is in the same county. If the backup site is in a different county, or even a neighboring state, get a second license for that location as well. Otherwise, you might be stuck in a rain with a very few guests, trying to get through the ceremony before loading up your drenched self and heading to the reception -- where most sensible guests will have been waiting the entire time.
Every county is different...
Different counties in Illinois have different requirements, so contact the specific county for more information before applying for the license. For the ceremony itself, some counties require witnesses and some (including Rock Island County) do not, so factor that in if it is an issue.
