In the Chicago suburbs, I get my feed at Ludwig's Feed Store in Lemont.
The only issue I have with Ludwig's that you have to check the tags when they bring you the bags. They often mix up the bags of food. Also, they run out. Wednesday is when they get new shipment. I've found that calling ahead doesn't really help. Also the GBS has antibiotic. I've asked them to get it without, and they gave me a strange look (it comes WITHOUT?!?!) and then said no. Since I only get a bag or 2 every other week, I've dealt with it.
There's a feed store in Summit, called, The Feed Store (how clever!). Don't buy from there. I've gotten feed and it was buggy. I mean, the bugs were exiting the bag in my car. A bug here or there can't be helped, but this was excessive.