When Illinois seperated from the Indiana Territory on Feb. 3, 1809, its government was prescribed by the Northwest Ordinance of 1787. Under that Act, the President of the United States appointed a territorial Governor and three territorial judges, who in addition to their executive and judicial responsibilities, served as the legislative branch in an unicameral body called the Council of Revision. All legislation written by this Council was subject to Congressional approval. When Illinois became a territory of the second grade in 1812, citizens elected a House of Representatives, from which members were chosen for an upper chamber known as the Legislative Council, and these two chambers comprised the territorial General Assembly that replaced the Council of Revision as the territory's legislative body.
From the description of Minutes of the Council meetings, 1809-1812. (Illinois State Archive). WorldCat record id: 35641203
