Consumption: No, Possession: Yes (with limitations)
The Illinois state law legalizing recreational cannabis starting January 1, 2020 does not allow for consumption of cannabis (also known as marijuana, pot or weed) in public. Smoking or consuming cannabis flower, concentrates and infused products is prohibited in the Forest Preserves. Anyone caught consuming cannabis in the Forest Preserves will be cited and may be subject to administrative or criminal penalties.
You may possess cannabis in the Forest Preserves, subject to the Illinois recreational cannabis possession limits. Anyone in violation of the Illinois recreational cannabis possession limits will be cited and may be subject to administrative or criminal penalties (unless they possess a valid Illinois medical cannabis registry identification card or a similar form of patient identification from another state where medical cannabis is legal).
The legal age for cannabis consumption and possession in Illinois is 21 years old. Anyone under 21 years old and in possession of any amount of cannabis will be cited and subject to administrative or criminal penalties (with medical registration exemptions). Anyone under 18 years old will have a parent or guardian notified of the citation.