In 2026, 12.7% of the state legislative incumbents running for election in Illinois will face primary contests, down from 14.4% in 2024 and the lowest percentage since 2016, when 11.8% of incumbents faced primaries.
In total, 18 incumbents face contested primaries across the Illinois House and Senate. The average number of incumbents contested each election cycle since 2010 was 21. Of the 18 incumbents in contested primaries, 11 are Democrats and seven are Republicans.
Illinois has 33 contested state legislative primaries in 2026, an 18% increase from 28 in the preceding cycle.
Nineteen of these primaries are for Democrats, up 12% from 17 in 2024. Republicans have 14 primaries, a 27% increase from 11 in 2024.
In total, 282 major party candidates—157 Democrats and 125 Republicans—filed to run. All 118 House seats and 39 of 59 Senate seats are up for election. Fifteen of those seats are open, meaning no incumbents filed. Six seats were open in 2024.
Illinois has had a Democratic trifecta since 2003, except during the Republican governorship of Bruce Rauner from 2015 to 2019. Democrats currently have a 78-40 majority in the House and a 40-19 majority in the Senate.
Illinois’ state legislative primaries are scheduled for March 17.
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