This issue was authorized by Congress on 1 June, 1918 to commemorate the Centennial of the admission of Illinois to the union in 1818. The Act authorized the minting of 100,000 coins with an additional 58 struck and put aside for assay.
The obverse design was done by George T. Morgan as chief engraver at the mint (Charles Barber having passed away in 1917). The youthful, Beardless face which dominates the obverse design was modeled from a photograph of the Statue that Andrew O’Connor created for the Illinois Centennial. That statue stands in Springfield. The inscription “CENTENNIAL OF THE STATE OF ILLINOIS” runs around the outer edge of the coin from 9 O’clock to 4 O’clock with the words separated by dots. The date 1918 is under the bust were Lincoln's shoulder would be, while the word “LIBERTY” is in front of the bust just below Lincolns Adams Apple. “IN GOD WE TRUST” in a small block font is behind Lincolns head & neck. The final interesting feature is the use of beads & pellets in place of denticles along the rim.
The reverse was designed and engraved by then assistant engraver John R. Sinnock. The design is derived from the Illinois State Seal and shows a rather fierce eagle with one talon on a rock, the other on a Union Shield that rests on an olive branch. The Eagle holds a ribbon in his beak with the State motto “UNION, NATIONAL SOVEREIGNTY, STATE” inscribed upon it. The rock stands on the shore of a lake (Lake Michigan perhaps) and faces west away from the sun as it rises from the lake. The motto “E PLURIBUS UNUM” is directly above the sun. “UNITED STATES OF AMERICA“ arcs across the top (with dots separating the words as on the obverse) and “HALF DOLLAR” across the bottom. There is no dot between Half & Dollar but there is a dot at the either end of the inscription separating it from the United States of America inscription. Finally the beads & pellet rim border is also present on the reverse.