The Illinois General Assembly is the legislative branch of the state of Illinois in the United States, created by the first constitution adopted in 1818. It works beside the executive branch led by the state governor and the judicial branch led by the supreme court. The Illinois General Assembly is comprised of the Illinois House of Representatives which serves as the lower chamber and the Illinois Senate which serves as the upper chamber. The Illinois House of Representatives is made of 118 representatives elected from individual legislative districts to two-year terms. The Illinois Senate is made of 59 senators. In order to avoid complete turnovers in senate membership, some legislative districts elect senators to two-year terms while others elect senators to four-year terms.

The Illinois General Assembly convenes at the Illinois State Capitol in Springfield, Illinois. Its first official working day is the second Wednesday of January each year. Its primary duties are to pass bills into law, approve the state budget, confirm appointments to state departments and agencies, act on federal constitutional amendments and propose constitutional amendments for Illinois. It also has the power to override gubernatorial vetoes through a three-fifths majority vote in each chamber.