A party may direct written interrogatories to any other party. A copy of the interrogatories shall be served on all other parties entitled to notice.Interrogatories are written questions that one party sends to the other. The receiving party is required to answer these questions under oath. A Practice Note discussing the structure and content of interrogatories in Illinois circuit court civil litigation under Illinois Supreme Court Rule 213. A sample response to interrogatories that may be used in discovery in Illinois circuit court litigation. A party may serve on any other party no more than 25 written interrogatories, including all discrete subparts. The process of obtaining information during the legal process is referred to as discovery. Each party is required to respond truthfully and completely. Fill in the "certificate of service" on the last page before mailing them back to the other side.