There's a teacher at Joel Hall in Andersonville called Tonna.  She's very good and patient, and has a good knowledge of anatomy.  She has Sunday classes, too.

At Lou Conte's, the Saturady classes with Paul are good, but you probably should have some basic ballet before his classes.  He also teaches in Naperville.

The Chicago Ballet on Wabash has some good classes, I am told; never tried them due to the problems parking in the Loop.

Ruth Page on Dearborn has some very good teachers.  I take several classes there.  Some dancers think there's too much "attitude" there however, but I've never noticed it.

If you've had basic ballet and want something challenging and different, try DePaul university's athletic center for Thursday night and Saturday classes from Dimitri Roudenev.  He's one of the best Russian/Vaganova teachers in Chicago.

If you're in the suburbs, it's a question of which suburb.  Academy in Oak Park, with Iris.  Northwest Academy.  Evanston.  Salt Creek in Hinsdale is good, but the classes are "fast," at least for me.

Good luck! Post another message on this board to let me know what you've decided.