In your petition, clearly explain why you are being held illegally. Federal habeas corpus is available for a state prisoner when a federal constitutional violation makes custody, or its conditions, unlawful.Though subject to different rules, incarcerated people in both state or federal custody may petition for a federal writ of habeas corpus. What Is Habeas Corpus? Any federal court may grant a writ of habeas corpus to a petitioner who is within its jurisdiction. 251 (1947); A Study of the Illinois Supreme Court, is Univ. Chi. All forms are ADA accessible, and you can handwrite or type into the PDF form to fill it out. Suggestions? Appellate Court Forms. The Illinois Supreme Court is the highest court in the State.