The obverse, depicting Abraham Lincoln, was designed by Chief Engraver George T. Morgan; the reverse, based on the Seal of Illinois, was by his assistant and successor, John R. Sinnock.

A commemorative was wanted by the State of Illinois to mark the centennial of its 1818 admission to the Union, and in 1918, legislation was introduced into Congress to accomplish this.

Neither had any objection to the legislation, though McAdoo had explained that the problem with commemorative coins was that they did not sell as well as expected, and many were returned to the Mint for melting.

After telling of his meeting with the officials, Wheeler explained to the committee that the coins would be purchased by the State Treasurer of Illinois and so there would be no returns.

Ashbrook then asked if the coins were to be sold at a premium by the centennial committee, and Wheeler denied this, indicating that they were to be circulated like any other half dollar.

[4] On March 12, Ashbrook submitted a report on behalf of his committee recommending passage of the bill once it had been amended to reduce the authorized mintage from 200,000 to 100,000 and to add a statement that the United States government would not be responsible for the cost of the dies.

He was quizzed by North Carolina's Claude Kitchin, who asked whether there had been a unanimous recommendation by the committee, whether McAdoo and Baker had approved the bill, and whether there was precedent for a half dollar in honor of a state's centennial (there was not).

Later in the day, Illinois Senator James Hamilton Lewis made a statement which was inserted in the Congressional Record at this point, applauding the passage of the honor to his home state, and noting that "more than a hundred thousand of her sons" were then being deployed to the battlefields of World War I.

Anthony Swiatek and Walter Breen suggested "their presence on a coin designed during the concluding months of World War I might have been considered just a bit raw".

[10] The reverse also bears the legends, UNITED STATES OF AMERICA, E PLURIBUS UNUM (the national motto, meaning "out of many, one") and HALF DOLLAR.

McAdoo "specifically direct[ed]" that the Illinois state motto be deleted from the scroll in the eagle's beak on the reverse, to be replaced with the national one.

Q. David Bowers deemed Sinnock's reverse "the finest work he ever did for a legal tender coin", not excluding the Roosevelt dime (1946) and Franklin half dollar (1948, posthumous).

[18] He noted of Sinnock's reverse, "the little burst of sun at the right is almost a bow to the Roty–Saint-Gaudens–Weinman developments outside the Philadelphia Mint in American numismatic taste and iconography in the generation following 1900.

None of our previous souvenir coins has been for the purpose of commemorating an occasion, event or undertaking that was confined entirely by the boundaries of a single state.

A total of 100,058 Illinois Centennial half dollars were struck at the Philadelphia Mint during August 1918, with the excess over the round number reserved for inspection and testing at the 1919 meeting of the annual Assay Commission.

The centennial commission distributed them, at face value, to its county affiliates in proportion to their share of Illinois' population, on condition they be sold at a premium to help pay for local celebrations, and if one had already been held, for war relief.