With this story, Giv. J.B had already approved the legalization earlier in the morning of May 31st. The House of Representatives voted 66-47 to allow possession and sales beginning Jan. 1, 2020. Which would make Illinois the 11th state to legalize cannabis and the first state in which a legislature approved commercial sales. Illinois residents age 21 and over may possess up to 30 grams or about 1 ounce of flower 5 grams of cannabis concentrate, or 500 milligrams of THC the chemical that gets users high in a cannabis-infused product such as gummies and other candy, tinctures and lotions. Adult visitors to the state may possess up to 15 grams of marijuana.