The Office of the State Appellate Defender is a state agency created by the State Appellate Defender Act (725 Illinois Compiled Statutes, Act 105). The principal function of the Office of the State Appellate Defender is to represent indigent persons on appeal in criminal cases when appointed by the Illinois Supreme Court, the Appellate Court or the Circuit Court.

To provide for this legal representation, the State Appellate Defender has district offices in each of the five appellate court districts of Illinois (Chicago, Elgin, Ottawa, Springfield and Mt. Vernon). The Supreme Court Unit, which is primarily responsible for representation in death penalty cases on appeal, is located in Springfield. The Capital Post-Conviction Unit, with offices in Springfield and Chicago, represents death row inmates in post-conviction proceedings.

The Capital Trial Assistance Unit is staffed with attorneys who provide trial assistance in death penalty cases in which the defendant is indigent. The unit, which has offices in Springfield, Chicago and Belleville, also provides assistance by expert witnesses, investigators, and mitigation specialists.

The Office of the State Appellate Defender is nationally recognized for excellence in providing indigent criminal services. In 1986, OSAD was honored by the American Bar Association and the National Legal Aid and Defender Association as the outstanding Public Defender office in the nation.