The Illinois General Assembly is the legislature of the U.S. state of Illinois. It has two chambers, the Illinois House of Representatives and the Illinois Senate. The General Assembly was created by the first state constitution adopted in 1818.

Under the Illinois Constitution, since 1983 the Senate has had 59 members and the House has had 118 members. In both chambers, all members are elected from single-member districts. Each Senate district is divided into two adjacent House districts.

The General Assembly meets in the Illinois State Capitol in Springfield, Illinois. Its session laws are generally adopted by majority vote in both houses, and upon gaining the assent of the Governor of Illinois. They are published in the official Laws of Illinois.

Two presidents of the United States, Abraham Lincoln and Barack Obama, began their political careers in the Illinois General Assembly–– in the Illinois House of Representatives and Illinois Senate, respectively.

Members of the House of Representatives are elected to a two-year term without term limits.

Members of the Illinois Senate serve two four-year terms and one two-year term each decade. This ensures that Senate elections reflect changes made when the General Assembly is redistricted following each United States Census. To prevent complete turnovers in membership (except after an intervening Census), not all Senators are elected simultaneously. The term cycles for the Senate are staggered, with the placement of the two-year term varying from one district to another. Each district's terms are defined as 2-4-4, 4-2-4, or 4-4-2. Like House members, Senators are elected without term limits.