Historical coats of arms of the U.S. states date back to the admission of the first states to the Union. Despite the widely accepted practice of determining early statehood from the date of ratification of the United States Constitution, many of the original colonies referred to themselves as states shortly after the Declaration of Independence was signed on 4 July 1776. Committees of political leaders and intellectuals were established by state legislatures to research and propose a seal and coat of arms. Many of these members were signers of the Articles of Confederation, Declaration of Independence, and United States Constitution. Several of the earliest adopted state coats of arms and seals were similar or identical to their colonial counterparts.

The Great Seal of the State of Illinois is the official emblem of the U.S. state, and signifies the official nature of a document produced by the state of Illinois. The flag of the state of Illinois consists of the seal of Illinois on a white background, with the word "Illinois" underneath the seal. The present seal was adopted in 1869, the flag bearing the central elements of the seal was adopted in 1915, and the word Illinois was added to the flag in 1970. In a 2001 survey by the North American Vexillological Association, the flag of Illinois was ranked 49th out of 72 different flags of states and territories, mainly in the US and Canada.