The 2018 Cook County Board of Commissioners election was held on November 6, 2018, and was preceded by primary elections held on March 20, 2018. It saw all seventeen seats of the Cook County Board of Commissioners up for election to four-year terms and coincided with other 2018 Cook County, Illinois, elections (including the election for president of the Cook County Board of Commissioners).
Anticipating a potential wave election year for Democrats, President of the Cook County Board of Commissioners and Cook County Democratic Party Chairwoman Toni Preckwinkle made a focused effort to increase the Democrats' majority on the Cook County Board of Commissioners, focusing these efforts on three of the Board's four Republican-held seats. Preckwinkle-backed Democratic nominees ultimately succeeded in ousting Republican incumbents in the 14th and 15th districts, but fell roughly a mere 2,000 votes shy of unseating the 17th district's Republican incumbent. Preckwinkle did not target the Republican-held 9th district seat, as the incumbent Republican, Peter N. Silvestri, was both popular and a political centrist and had a reputation for being a peacemaker on the Board at times when conflict arose between its members. Democrats ran candidates for all seventeen seats, compared to the fifteen seats that the party had contested in the preceding 2014 election. Meanwhile, Republicans ran candidates for eight seats, and increase from the five seats they had contested in the 2014 election.
Seven new members were elected, and ten incumbents were reelected. Three incumbents did not seek reelection. Four incumbents lost reelection, with two being defeated in primaries and the other two losing their general elections.
Two races saw seats change party, in both instances seeing an incumbent Republican losing to a Democratic challenger, creating a net gain of two seats for Democrats and a net loss of two seats for Republicans. Nine races saw a Democrat unchallenged in the general election.
1st district
Incumbent first-term Commissioner Richard Boykin, a Democrat, lost reelection, being unseated in the Democratic primary by Brandon Johnson by a margin of 0.88%. Johnson went on to win the general election unopposed.
Primaries
Democratic
Republican
Only write-in candidates ran in the Republican primary. No certified write-in received enough votes to win the nomination.
General election
2nd district
Incumbent Commissioner Dennis Deer, who was appointed in 2017 to fill the vacancy left by the death in office of Robert Steele, won election to his first full term.
Primaries
Democratic
Republican
No candidates, ballot-certified or formal write-in, ran in the Republican primary.
General election
3rd district
Incumbent Commissioner Jerry Butler, a Democrat who first assumed the office in 1985, did not seek reelection. Democrat Bill Lowry was elected to succeed him.
Primaries
Democratic
Republican
No candidates, ballot-certified or formal write-in, ran in the Republican primary. Republicans ultimately nominated George Blakemore.
General election
4th district
Incumbent Commissioner Stanley Moore, a Democrat who was appointed to the office in 2013 and was elected outright to a full term in 2014, won reelection to a second full term.
Primaries
Democratic
Republican
No candidates, ballot-certified or formal write-in, ran in the Republican primary.
General election
5th district
Incumbent sixth-term Commissioner Deborah Sims, a Democrat, was reelected.
Primaries
Democratic
Republican
No candidates, ballot-certified or formal write-in, ran in the Republican primary.
General election
6th district
Incumbent Commissioner Edward Moody, a Democrat who was appointed to the seat in 2016 following the death in office of Joan Patricia Murphy, did not seek reelection. Democrat Donna Miller was elected to succeed him.
Primaries
Democratic
Donna Miller defeated Patricia Joan Murphy, the daughter of deceased former 6th district commissioner Joan Patricia Murphy and Crestwood mayor Louis Presta.
Republican
No candidates, ballot-certified or formal write-in, ran in the Republican primary.
General election
7th district
Incumbent second-term Commissioner Jesús "Chuy" García, a Democrat, did not seek reelection, instead opting to run for election to Illinois's 4th congressional district. Democrat Alma Anaya was elected to succeed him.
