The backdrop of the city of Chicago and the gray color stands for the industrial wealth of the city and its importance to the county.
The circle represents the unity, bordered with railroad tracks and the strong connections to the railroad industry.
The bottom half inside the circle is a deeper blue, symbolizing Lake Michigan. The top half is a rich green, representing the forest preserves and the natural beauty of the county.
The five yellow points harmoniously arranged outside the circle are meant to represent the five districts of the county, separate bright points in concordance with the same body.
The county itself is the focus of the flag, and yellow was chosen to symbolize hope for an ever better future, reminiscent of sunlight.
Red symbolizes life and vigor, while also pointing to the history of the county, by displaying the founding date.