According to The Cook County Album of Genealogy, Francis Schweinfurth Sr., who had emigrated with his family from Germany, was a factor in creating the Illinois Republican Party.

Many early members of the party failed to gain statewide office or election to the United States Congress due to this anti-slavery view, although this early position of the party in Illinois would later propel several candidates to prominent office, including the Governorship of Illinois won by Richard Yates, and in the mid-1850s, the election of former Chicago Mayor James Hutchinson Woodworth to one term in the United States House of Representatives.

Frank Schweinfurth, according to the Cook County Album of Genealogy, was a major force in nominating Abraham Lincoln.

The last time Republican carried in presidential elections was 1988, when George H. W. Bush won Illinois by 2.1% marginal points.

While this tendency has helped Illinois GOP candidates in the suburbs, it has alienated many conservative voters downstate.

Republican nominee Bill Brady narrowly lost the gubernatorial election to Pat Quinn, leaving Democrats in full control of the redistricting process.

In 2014, Tim Schneider, who was a member of the Cook County Board of Commissioners, was named the chairman of the state party.

B. Pritzker in a landslide with the party also losing two congressional seats (Roskam and Hultgren) and becoming a superminority in the state legislature.

[1] The 2020 Elections saw a moderate swing back to the party in terms of votes, however this did not lead to major seat gains.

However State Supreme Court Justice Thomas L. Kilbride was defeated in his bid for retention with the intention of flipping the seat to the Republicans in 2022.

As of 2023, Republicans control the mayor's offices in four of Illinois's ten largest cities:[citation needed]