Year Adopted: 1915, 1969 revision. White flag with the state flag emblem in the center, the word "ILLINOIS" underneath. Illinois was admitted as the 21st U.S. State in 1819.

Illinois had an earlier official state flag. The first was adopted on July 6, 1915, after a design contest sponsored by the Daughters of the American Revolution. A bill to amend the original flag act of 1915 was passed by the General Assembly and became effective July 1970. It modified the design, specified colors to be used, and added the word "Illinois" underneath the seal.

On a white field the flag displays elements from the state seal; a rock on a stretch of land with water and the rising sun behind it, and a shield bearing the national stars and stripes in the claws of a bald eagle. A ribbon in the beak of the eagle bears the state motto “State sovereignty—national union”. The dates 1818 (for statehood) and 1868 (for the first use of the state seal) are shown on the rock beneath the eagle.