The 1924 United States Senate election in Illinois took place on November 4, 1924.
Incumbent Republican Medill McCormick was unseated in the Republican primary by Charles S. Deneen, who went on to win the general election.
The primaries and general election coincided with those for other federal elections (president and House) and those for state elections. The primaries were held April 8, 1924.
This was the first election for this U.S. Senate seat to be held after the Nineteenth Amendment to the United States Constitution granted women suffrage.
Deneen won by a mere 0.69% margin of just 5,944 votes.
On February 25, 1925, as he was preparing to leave office, McCormick died in what is considered to have been a suicide (though the suicidal nature of his death was not known to the public, contemporarily). His reelection loss is believed to have contributed to his suicide. McCormick's widow Ruth Hanna McCormick would go on to defeat Deneen in the 1930 Republican primary.