Children as young as 13 say they drank alcohol in the last 30 days in Will County, according to the latest Illinois Youth Survey.
It found that 16% of 8th graders said they had consumed alcohol in the past month, and that rose to 29% over the past year.
The rate has fallen since the previous survey in 2016.
The survey gathers information every two years on substance abuse among young people. Students in the 8th, 10th and 12th grades are asked about their consumption of alcohol.
Among sophomores 22% said they had drunk alcohol in the past month. The figure jumps to 37% for the past 12 months.
And 45% of seniors admitted drinking alcohol in the previous 30 days.
The information in the survey is used to plan substance abuse prevention programmes across the state.
The legal drinking age is 21. The survey does not reveal whether any of the alcohol consumption took place at home, under parental supervision, which is allowed under Illinois law.