Easy. We're in the middle:
We recommend flying into either Midway airport (Chicago, 2.5 hours north of us), or Indianapolis airport (south of Indy, 2 hours east of us), and then taking ground transport the rest of the way. Chigago-O'Hare is not a bad option, but it is farther away than you think (3+ hours north of us) and driving from there to Urbana involves going the long way through the entire city of Chicago.
Some time-zone trickery: Indy is 1 hour later than Champaign, so beware of late arrivals or early departures.
Smaller airports in the area include Bloomington-Normal (45 minutes from us by car) and Champaign (10 minutes from us by car). There are not many flights out of either of these, but sometimes you can get a good deal, so it’s worth checking anyway. If you fly through Champaign, be aware that we've noticed an awful lot of delayed or canceled flights lately. Don't panic, but do be prepared for a chance of unwanted rebooking.
From Chicago: Amtrak is comfortable and moderately punctual. Greyhound is slightly less comfortable and quite a bit more reliable.
From Indy: Your best bet is to rent a car. Ground transport is iffy at best!
From Bloomington: Your best bet is to rent a car. We may also be able to coordinate a ride for you—get in touch if you're interested.
From Champaign airport: cabs are plentiful and cheap.
If you might want to carpool down from Chicago, let us know and we can likely put you in touch with a buddy to share the ride with.
There is a decent bus system and most of the city is easily walkable. No need to rent a car, unless you really want to.