Court Supervision is the Illinois equivalent of (most of) Missouri's SIS. The defendant is found guilty (or pleads guilty), but the conviction isn't formally entered. Instead, the case is placed on supervision for a set period during which the defendant must comply with conditions.
Successful completion of supervision results in the case being dismissed without a conviction. The arrest and supervision still appear on certain background checks, but the technical absence of conviction matters for employment, licensing, and immigration purposes.
Court Supervision is available for many misdemeanors and traffic offenses in Illinois. It's not available for DUI second offenses, certain Class A misdemeanors with mandatory minimums, or any felony. First-time DUIs are eligible.