Illinois is one of only 10 states that do not define "reasonable doubt" for juries.
Illinois courts have a well-established precedent to refrain from defining for juries what "beyond a reasonable doubt" means. The principle also is baked into the Illinois Pattern Jury Instructions-Criminal, which informs trial courts to not provide a definition instruction, stating: "reasonable doubt is a term which needs no elaboration and we have so frequently discussed the futility of attempting to define it that we might expect the practice to be discontinued."