The State of Illinois wanted a commemorative coin to be issued for the centennial of its 1818 admission to the Union. A bill that would accomplish this, H.R. 8764, was introduced into the U.S. House of Representatives on January 16, 1918 by that state's Loren E. Wheeler. It was referred to the Committee on Coinage, Weights, and Measures, which held hearings on March 5. Wheeler told the committee (of which he was not a member) that the coins were desired for distribution during the celebrations in Illinois. He had been to see Treasury Secretary William G. McAdoo and Mint Director Raymond T. Baker. 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. James L. Slayden of Texas asked what the cost to the federal government would be, but Wheeler did not know. Slayden asked what had been the cost for the 1916–1917 McKinley Birthplace Memorial dollar, and Ohio's William A. Ashbrook, the chairman of the committee, said that the cost of the dies had been borne by the group purchasing the coins from the government; Ashbrook proposed amending the bill to make this clear this would be an expense to be paid by Illinois. Wheeler had no objection, and stated that to avoid returns, it might be best if the issue was limited to 100,000 coins rather than the 200,000 in the original bill. 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. This concluded the public hearing on the bill, with the committee to take further action in executive session.
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.
Wheeler presented the bill on the floor of the House of Representatives on April 6, 1918. 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). Wheeler reassured Kitchin as to the unanimity of the committee, and the approval by the officials, but did not answer the centennial question definitively, instead citing instances of prior commemorative issues (the Louisiana Purchase Exposition dollar and the Panama-Pacific commemorative coins). Ashbrook intervened, assuring Kitchin that his committee had unanimously approved it. Kitchin had no more questions, and the House approved the bill without a recorded vote.
H. R. 8742 was transmitted to the Senate, where it was referred to the Committee on Banking and Currency. That committee's chairman, Oklahoma's Robert L. Owen, reported it back with an amendment to the full Senate, where the bill was considered on May 21, 1918. The House-passed bill had said the laws relating to the minor coinage of the United States (the cent and nickel) would apply to the coin; this was changed to state that the laws relating to the subsidiary silver coinage (which the half dollar was) would apply. The bill was passed as amended without objection. 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.
Since the versions the two houses had passed were not identical, the bill returned to the House of Representatives, where on May 25, Arizona's Carl Hayden successfully moved that the House agree to the Senate amendment. The Speaker, Champ Clark, felt that the title of the bill might have to be changed for reasons he did not explain, but Hayden disagreed and Clark did not press his point. The bill passed the House, and was enacted by the signature of President Woodrow Wilson on June 1, 1918.