Due to the state's failure to redistrict, all of the seats were elected at-large by plurality block voting, with voters choosing up to 177 candidates to support.

For the 1960 redistricting cycle, the state's governor was Democrat Otto Kerner Jr., while both chambers of the legislature were controlled by Republicans.

The legislature elected in 1964 pushed for governmental reform, starting the process that eventually led to the 1970 rewrite of the Constitution of Illinois.

[r 1]: 292–294  In the 1930s, there were various efforts supported by governors Louis L. Emmerson and Henry Horner to allow Cook County proportional representation in either the Illinois House of Representatives or the Illinois Senate, while limiting its representation in the other, but these proposals died due to strong bipartisan opposition from downstate politicians.

[r 1]: 294–295 By 1953, William Stratton, the newly elected governor of Illinois, viewed redistricting as a priority amidst increasing public pressure over malapportionment.

[n 2] The redistricting commission deadlocked over a similar issue to what prevented a bipartisan map from passing the legislature – namely, the number of districts in Chicago.

[r 1]: 300 [n 4] Starting on November 14, the Republicans on the commission began boycotting the meetings due to Democrats' insistence that Chicago control 23 districts.

[n 3] Negotiations continued up until the deadline, with Democrats eventually proposing a map with only 22 Chicago-based districts, but the commission ultimately could not reach a compromise.

This lawsuit was initially dismissed by Sangamon County Circuit Court judge Dewitt S. Crow on July 16.

Secondly, a lawsuit filed by Chicago lawyer Gus Giannis argued that an at-large election also had to take place for the State Senate.

[n 8] In response to this case, Attorney General Clark issued a ruling stating that an at-large election would be required for the Senate as well.

[p 2][r 1]: 300 Following the court's decisions, Kerner called a special session of the legislature on January 6 to set up procedures for the at-large election.

[r 1]: 301–302 [n 12] An initial bill was passed unanimously by the House, but sunk by Republicans in the Senate over concerns that each party would choose to nominate fewer than 118 candidates, leading to an uncompetitive election unfairly favorable to incumbents.

The Republican convention, held at a local Elks Club building, was controlled by delegates loyal to Charles H. Percy, the party's candidate for governor.

The Democratic convention, held at the St. Nicholas Hotel, delegated the responsibility for preparing a slate of candidates to an executive committee.

Incumbent legislators were placed at the top, ordered by seniority, alternating between candidates from Cook County and downstate.

The Field Enterprises newspapers,[d] the Chicago Tribune, the Champaign News-Gazette, and the Illinois State Journal endorsed the Republican slate.

[r 4][n 18] Likewise, the Daily Herald, a newspaper serving the suburbs of Chicago, endorsed seven candidates (four Republicans and three Democrats) who they believed had a good understanding of suburban issues.

[n 25] Based on early reported returns in some downstate precincts, Democrats declared victory on November 4, predicting that they had elected their entire slate.

[n 27] Unofficial results for 100 counties, excluding Cook and DuPage, were reported on November 26, showing a strong performance by Democrats.

[n 28] Unofficial statewide results were reported on December 3, showing that every Democratic candidate had won, with many Republican incumbents losing re-election.

[n 29] Five Republican candidates[f] obtained an injunction over the results in DuPage County, claiming that there were errors in the vote count in five precincts.

[n 32] On December 14, Democratic Attorney General William G. Clark filed a motion to move the case to the Illinois Supreme Court, to force the vote count to be released.

[n 19] However, voters who did not vote only straight-ticket had a significant impact as well: they determined the 59 Republicans who were elected, as well as the order of the winning Democratic candidates.

While Republicans maintained control of the Illinois Senate, Democrats held the governorship and won a two-thirds supermajority in the State House.

[n 34] The election of many "blue ribbon" candidates in both parties led to a focus on governmental reform, especially improvements to the operation of the legislature.

There was again difficulty in passing maps, with downstate and Chicago legislators not wanting to give up representation in favor of the suburbs, which had grown their relative share of the population.

[r 8][n 35][p 4] The resulting maps were relatively fair to both parties, although they caused a significant shift of power from downstate to the Chicago area.

[r 8]: 18  The tie-breaking member would only be added if the commission deadlocked, and would be randomly chosen by the Secretary of State, with one candidate nominated by each party.

[h][n 36] The 1964 election helped launch the political careers of certain Democrats, including Adlai E. Stevenson III, who later represented Illinois in the U.S. Senate, and Harold Washington, who eventually became mayor of Chicago.