The flag has a white background, and much of the Illinois state seal is pictured in the center. There is a bald eagle perched on a rock holding a red, white, and blue shield in its talons (the stars are white on a blue background and the stripes are red and white). The shield has 13 stripes and 13 stars, representing the original 13 colonies of the USA. The eagle is holding a banner in its beak which reads "STATE," "SOVEREIGNTY," "NATIONAL," and "UNION." The word sovereignty is upside down. The rock has the dates 1818 and 1868 written on it; 1818 refers to the year Illinois became a state and 1868 refers to the date the state seal was redesigned.

Illinois was the 21st state in the USA; it became a state in 1818.