According to Illinois state law, Illinois residents can purchase up to 30 grams (one ounce) of marijuana flower, 5 grams of extract or concentrate, and 500 mg of THC in an infused product (edibles), per day at one store. Non-residents can purchase 15 grams (half-ounce) of marijuana flower, 2.5 grams of extract or concentrate, and 250 mg of THC in edibles. These totals are cumulative, so you can purchase up to the limit of each form of cannabis at the same time.