1980 United States presidential election in Illinois

The 1980 United States presidential election in Illinois took place on November 4, 1980. All 50 states and The District of Columbia, were part of the 1980 United States presidential election. State voters chose 26 electors to the Electoral College, who voted for president and vice president. Illinois voters chose between the Democratic ticket of incumbent president Jimmy Carter and vice president Walter Mondale, and the Republican ticket of Ronald Reagan and running mate George H. W. Bush, as well as the independent candidacy of John B. Anderson and running mate Patrick Lucey.

Illinois had voted Republican in the previous three presidential elections, and early analysis suggested that Reagan was a strong candidate against Carter in Dixie Southern Illinois. Nonetheless, at the beginning of the campaign trail one opinion poll suggested Reagan would lose to Carter by 26%, but the Republican campaign knew carrying a state which Gerald Ford had won four years ago to be essential and the state was heavily targeted by GOP campaigners. By mid-September, polls were showing Illinois as very close, and Carter was hit by political conflicts in Chicago between mayor Jane Byrne and State Senator Richard Daley.

Carter strategists did target the state in September and hoped that prospective Republican nominee John Anderson – who had run against Reagan in the Republican primary before launching his own independent presidential campaign – would take enough votes from Reagan for Carter to obtain a narrow victory. Polls in mid-October suggested that Illinois was "too close to call", and as election day neared, opinions fluctuated especially in the critical southern part of the state.

Ultimately Illinois—the state where Reagan was born and raised, and where Anderson served as a Congressman—was carried by the Republican ticket by a 7.93% margin of victory over the Democrats. Reagan won all but three counties, although Carter's 268,000-vote margin in massively populated Cook County meant Illinois nonetheless voted roughly 1.77% more Democratic than the nation at-large. Despite being Anderson's home state, the independent only won 7.30% of the popular vote in Illinois, or 346,754 votes, and he failed to carry any counties.

This would be the last time that Rock Island County voted Republican, as it has since turned sharply to the Democratic Party.