This chapter explains what counts as driving under the influence in Illinois — alcohol, cannabis, and other drugs — and why Illinois' implied consent law means every driver has already agreed to chemical testing before ever getting behind the wheel.
The most-tested distinction is between a statutory summary suspension, an automatic civil action triggered by a failed or refused chemical test, and a DUI conviction, a separate criminal outcome with its own escalating revocation periods for repeat offenses.
A common mistake is assuming a blood-alcohol level under the legal limit means it's safe to drive — impairment, not just the number, is what the law actually punishes, and relief programs like the Monitoring Device Driving Permit exist only for eligible first-time offenders.
What's the difference between a statutory summary suspension and a DUI conviction?⌄
A statutory summary suspension is an automatic civil action the Secretary of State imposes after a failed or refused chemical test — it happens regardless of a criminal case. A DUI conviction is a separate criminal outcome that adds its own revocation period on top, with longer minimums for each repeat offense.
Does a blood-alcohol concentration under 0.08% mean it's legal to drive?⌄
Not necessarily. Illinois law allows a DUI conviction even below 0.08% if your driving ability was actually impaired — the legal limit is a threshold for automatic per se violations, not a guarantee of safety below it.
What is a Monitoring Device Driving Permit (MDDP) for?⌄
It lets an eligible first-time DUI offender keep driving during a statutory summary suspension, as long as a Breath Alcohol Ignition Interlock Device (BAIID) is installed and monitored on their vehicle.