The 1st Illinois General Assembly, consisting of the Illinois State Senate and the Illinois House of Representatives, met from October 4, 1818, to March 31, 1819, during the 1st two years of Shadrach Bond's governorship, at The Kaskaskia State House. The apportionment of seats in the House of Representatives was based on the provisions of the First Illinois Constitution. Political parties were not established in the State at the time.
It was succeeded by the 2nd Illinois General Assembly.
This list is arranged by chamber, then by county. Senators and Representatives were both allotted to counties roughly by population and elected at-large within their districts.
In accordance with the Constitution of 1818, the senators were divided by lot into two classes to retire in two and four years. The two-year group would therefore hold elections in 1820 (consisting of senators from Bond, St. Clair, Randolph, Jackson, Johnson/Franklin, White/Jefferson, and Edwards/Wayne counties).