A first-offense Illinois DUI is a Class A misdemeanor with maximum exposure of up to 364 days in county jail under 625 ILCS 5/11-501(c)(1). In practice, first-time offenders rarely receive jail time on a base misdemeanor DUI. Court supervision or conditional discharge with no jail is the typical Cook County outcome for a clean-record defendant. Jail exposure increases sharply with enhancements: the high-BAC enhancement at 0.16 or above triggers a mandatory minimum 100 hours of community service or 2 days in jail. A DUI with a child passenger under 16 causing great bodily harm becomes a Class 4 felony with 1 to 3 years in state prison. Aggravated DUI charges under 625 ILCS 5/11-501(d) carry mandatory prison time.
