Every 10 years, states redraw the boundaries of their congressional districts to reflect new population counts from the census. Illinois lost a congressional seat this decade after the 2020 census. Democrats drew a new map that will likely allow the party to win one more House seat while costing Republicans two. The new map has also led to two member vs. member primaries, pitting Democratic Reps. Marie Newman and Sean Casten against each other in the 6th Congressional District, as well as Republican Reps. Mary Miller and Rodney Davis in the 15th District.
How the districts voted in 2020, by presidential vote margin in percentage points
Old map 18 districts
Change in Democratic districts: 3+3D
Change in Competitive districts: -3-3C
Change in Republican districts: -1-1R
New map 17 districts(-1)
How the new map shifts voting power by demographic
Illinois loses one of its 18 seats in the House after the 2020 census. Under the new map, there is no longer a district where Black residents represent the majority. The 2nd District — which includes the southern suburbs of Chicago — was extended farther south and west so that no demographic holds a majority.
The group that represents the majority in each district
About the data
Sources: US Census Bureau, Edison Research, each state’s legislature or other redistricting authority, Voting and Election Science Team via Harvard University’s Dataverse
Methodology note: Vote margins for new congressional districts are determined by calculating precinct-level vote totals for each district. If a new district splits a precinct, block-level voting-age population is used to allocate that precinct’s votes to the new districts. Block-level demographic data from the 2020 census is reaggregated into each new district’s boundaries.