99chambers

U.S. House seat · lines in effect since 2022

Illinois's 12th District

A district of about 745,000 people, 24% of adults with a bachelor's degree. It votes R+43.9 relative to the nation for president.

Mike Bost (R) · since Jan 6, 2015Next election Nov 7, 2028The 2026 race →
IL-12

Source: 2026 results: civicAPI; boundaries: Census Bureau TIGER/LineUpdated Nov 7, 2026, 3:01 PM ET

Where it sits among all 435 seats

Every U.S. House seat by partisan lean, from most Democratic to most Republican. Lean is the seat's presidential vote on current lines, relative to the nation.

R+43.9417th most
Democratic
Most DemocraticMost Republican218th seat · the majority line75921341011138614171615IL-12

Labels below the bar mark 16 other seats in Illinois.

Source: 99chambers: 2024 and 2020 presidential results on current lines, relative to the nation (2024 weighted 3:1)Updated Oct 16, 2026, 5:19 AM ET

Every race on these lines

Results recomputed from precinct returns as if today's boundaries had always existed, so years compare like for like.

201620182020202220242026
U.S. SenateR+16.6No raceR+34.4No raceNo raceNo race
GovernorNo raceR+23.2No raceNo raceNo raceNo race
U.S. HouseNo raceNo raceNo raceR+50.0R+48.4R+39.3

Outlined: the race for this seat itselfBlank: no race that year

Source: 99chambers results archive: precinct results allocated to current lines; 2026: civicAPIUpdated Nov 7, 2026, 3:01 PM ET

Who lives here, compared

Grey bars show the spread of all 435 seats. Small marks are other seats in Illinois. The black marker is IL-12.

Adults with a bachelor's degree24% 13th pct · 17th of 17 in IL

Lower than 87% of seats.

White adults without a degree67% 97th pct · 1st of 17 in IL

Higher than 97% of seats.

Hispanic residents3% 5th pct · 16th of 17 in IL

Lower than 95% of seats.

Black residents5% 37th pct · 13th of 17 in IL

Lower than 63% of seats.

Asian residents1% 8th pct · 16th of 17 in IL

Lower than 92% of seats.

People per square mile52 12th pct · 16th of 17 in IL

Less dense than 88% of seats.

Source: Census Bureau, American Community Survey 2020–2024 5-year estimates, allocated to current linesUpdated Oct 13, 2026, 5:06 AM ET

Seats most like this one

Nearest seats on demographics, density and lean.

MO-4
25% college gradsR+42.3Held RVA-9
24% college gradsR+44.0Held RIL-15
26% college gradsR+40.3Held RWV-1
22% college gradsR+44.3Held R

Source: Census Bureau, American Community Survey 2020–2024 5-year estimates, allocated to current lines; 99chambers: 2024 and 2020 presidential results on current lines, relative to the nation (2024 weighted 3:1)Updated Oct 16, 2026, 5:19 AM ET

Who has held it

These lines took effect in 2022.

  1. Mike Bost (R)
    2023– · Won 2022 by 50.0, 2024 by 48.4, 2026 by 39.3

Source: Past results: 99chambers results archive (MEDSL, Klarner, state election offices)