It has been noted that pretty decent frozen custard can be found in very south oak park--the oak park vicinity probably being the ice cream capital of the chicago area. But it was asked where else can one find quality custard.
Of course, frozen custard of the quality found in st. louis or milwaukee is, well found in st. louis and milwaukee. i do know of one little slice of wisconsin that is spreading towards us like a band of killer bees. it is the culver's chain of custard and butterbugers (with trademark). Culvers delivers the butterfat in several chicago suburbs (see link below).
I know of one other decent custard place. on north state, around the corner from the division street bars, about across the street from barnes and noble, is a newly opened custard place. i like the way their custard falls in big slabs out of the custard machine into waiting pits, ala ted drewes, instead of swirled directly into a cone. this form of custard is more dense. i have visited twice. the first time the custard lacked the really lipcoating creaminess associated with good custard. the second time, i was much happier.