Subject matter jurisdiction defines a court’s power to decide a lawsuit involving a particular subject matter, and to render an enforceable judgment. A court generally has jurisdiction when the particular claim raised in the case is within its constitutional jurisdiction—as provided by the state constitution or the U.S. Constitution—or because jurisdiction has been mandated by the state legislature or the United States Congress.

In Illinois, subject matter jurisdiction refers to a court's authority to hear cases of a particular type or cases relating to specific subject matter. The Illinois Constitution and various statutes establish the scope of subject matter jurisdiction for different courts within the state. For example, the Illinois Circuit Courts are the state's trial courts of general jurisdiction and are empowered to hear a wide range of cases, including civil, criminal, probate, and family law matters. On the other hand, certain courts, such as the Illinois Appellate Court and the Illinois Supreme Court, primarily have jurisdiction over appeals. Additionally, some courts have limited jurisdiction, such as small claims courts for civil disputes involving limited monetary amounts. Federal courts, on the other hand, have jurisdiction as defined by the U.S. Constitution and federal laws, typically involving federal questions, diversity of citizenship, or other specific federal matters. It is important for a case to be filed in a court with proper subject matter jurisdiction, as a lack of it can result in a dismissal of the case.