My son goes to Apple Tree. We didn't begin until four, but that was a potty training thing. Last I heard there are still spots open for 3 year olds. The four year old classes are filled. I think Apple Tree has a nice balance of fun and learning. My four year old has learned some new skills there. It is pretty structured...so they get use to the school routine. They do fun things to keep it interesting especially in the winter like: mismatch day, parachute day, show and tell, even had a field trip to a pumpkin farm (parent provided transportation).
The Plainfield Park District also has a Preschool called the "Great Adventures" program. My friend goes there and likes it. They have two locations, one at St. Johns church next to the mall in Joliet and on at the Streams off of Frasier.
Even if they don't have spots, get on the wait list. Lots of 3 year olds back out just before school is to start due to potty training readiness or they just aren't ready for other reasons.
I find chains like Chesterbrook to be more of a daycare when I looked. I found them to be VERY expensive also. I know they have academics and if you go daily I think it works, but you can choose your schedule so I felt there would not be any continuity of what would/wouldn't be taught when. But I didn't send my son there, those were just my thoughts from my viewings of all the schools.
The Park District also has all by myself programs, but you won't know that until that brochure comes out...they do not plan too far in advance. Also, if the minumum number does not enroll it is cancelled...I have had MANY classes canceled due to that lately with Plainfield. It becomes frustrating.