The Supreme Court of Illinois is the state supreme court of Illinois. The courts authority is granted in Article VI of the current Illinois Constitution, which provides for seven justices elected from the five appellate judicial districts of the state (U.S. state): Three justices from the First District (Cook County (Cook County, Illinois)) and one from each of the other four districts. Each justice is elected for a term of ten years and the chief justice is elected by the court from its members for a three-year term.

The court has limited original jurisdiction and has final appellate jurisdiction. It has mandatory jurisdiction in capital (Capital punishment) cases and cases where the constitutionality of laws has been called into question, and discretionary jurisdiction from the Illinois Appellate Court. Along with the state legislature, the court promulgates rules for all state courts. Also, its members have the authority to elevate trial judges to the appellate court on a temporary basis. The court administers professional discipline through the Attorney Registration and Disciplinary Committee and they govern initial licensing through the Illinois Board of Admissions to the Bar.

The official reporter (Law report) of the Illinois Supreme Court is Illinois Reports.

While the justices of many states supreme courts are expected to relocate to the state capital for the duration of their terms of office, the justices of the Illinois Supreme Court continue to reside in their home districts and have chambers in their respective appellate courthouses (for example, the three First District justices are chambered in the Michael Bilandic Building in Chicago). The justices travel to Springfield to hear oral arguments and to deliberate. Accordingly, the Illinois Supreme Courthouse includes temporary apartments for the justices use while in Springfield.