Illinois’s 12th Congressional District is represented by Mike Bost (R) in the U.S. House of Representatives. The district is one of Illinois’s seats in the 435-member House of Representatives. After the 2020 Census, the average congressional district had 761,169 people, according to the U.S. Census Bureau, and these district boundaries were drawn during the redistricting cycle that followed.
Congressional representatives serve two-year terms and face election every even-numbered year. The next election for this seat will take place on November 3, 2026.
Population
748,190
Median Household Income
$66,758
Population and income: U.S. Census Bureau, American Community Survey 5-year estimates for 2019 to 2023, for district lines in effect on January 1, 2023.
Partisan Lean
R+44
2024 presidential margin (Trump vs Harris). Source: The Downballot.
District boundary, 119th Congress. Boundary data: U.S. Census Bureau TIGERweb. Map tiles: OpenStreetMap.
Mike Bost and Illinois's 12th Congressional District
Mike Bost, a member of the Republican Party, represents Illinois's 12th Congressional District and has held the seat since January 6, 2015. The boundary map for the district is above and the ZIP codes it covers are listed further down this page.
Committee assignments: House Committee on Transportation and Infrastructure, House Committee on Agriculture and House Committee on Veterans' Affairs.
The current term ends January 3, 2027. The seat is on the ballot on Tuesday, November 3, 2026. Washington office phone: 202-225-5661. Official site: bost.house.gov.
Current Representative
Rep. Mike Bost (R)
119th Congress • Republican • Representing this district since January 6, 2015
Mike Bost currently represents Illinois’s 12th Congressional District as a member of the Republican Party in the United States House of Representatives. The representative’s district office helps constituents with federal casework, such as Social Security claims and veterans’ benefits.
2026 Election
On the ballot November 3, 2026
- Julie Fortier, Democratic
- Mike Bost, Republican Incumbent
Source: Illinois State Board of Elections, general election candidate list, checked September 26, 2026. Write-in candidates are not listed.
Key dates for November 3, 2026
| Register by mail | Tuesday, October 6 PassedApplication must be postmarked by this date. |
|---|---|
| Register online | Sunday, October 18 |
| Register in person | Through Election Day, November 3 |
| Same-day registration | Grace-period registration and voting run through Election Day at early voting sites and polling places. |
| Early in-person voting | September 24 to November 2 Open nowSites and hours vary by election authority. |
| Request a mail ballot | Thursday, October 29 Mailed requests must be received by October 29. In-person requests are accepted until November 2. |
| Return a mail ballot | Postmarked by November 3 and received by November 17. Ballots delivered by hand or to a drop box are due by 7 p.m. on November 3. |
| Election Day | Tuesday, November 3, 2026 |
Check your registration with the Illinois voter lookup. Dates come from the Illinois election office and were checked September 26, 2026. States can change deadlines, so confirm with your election office before you act.
Polling places in Illinois are open 6 a.m. to 7 p.m., local time. Confirm your registration and polling place on the official federal voter page for Illinois: vote.gov.
What is on the ballot nationally on November 3, 2026
Contact Your Representative
Washington Office
352 Cannon House Office Building
Washington, DC 20515
Phone: (202) 225-5661
Online
Committee Assignments
- House Committee on Transportation and Infrastructure
- House Committee on Agriculture
- House Committee on Veterans' Affairs (Chair)
About This District
The district spans 34 counties in Illinois, including Monroe, Randolph, Jackson, Lawrence, and Clay, and others. Its largest cities are O'Fallon (about 32,000), Carbondale (about 22,000), Marion (about 17,000), and Mount Vernon (about 15,000).
Learn more about congressional districts
- What is a congressional district?
- What does a U.S. Representative do?
- What is gerrymandering?
- How congressional redistricting works
Frequently Asked Questions
Who represents Illinois's 12th Congressional District?
Mike Bost (R) represents Illinois's 12th Congressional District in the U.S. House of Representatives.
What political party is Mike Bost a member of?
Mike Bost is a member of the Republican Party.
How can I contact Mike Bost?
You can reach Mike Bost by phone at 202-225-5661 or through their official website at https://bost.house.gov.
When does Mike Bost's current term end?
Mike Bost's current term in the U.S. House of Representatives ends on January 3, 2027.
Where is Illinois's 12th Congressional District?
Illinois's 12th Congressional District is located in the state of Illinois and is one of the 435 voting congressional districts in the U.S. House of Representatives.
What district does Mike Bost represent?
Mike Bost has represented Illinois's 12th Congressional District since January 6, 2015. The boundary map for the district is on this page.
Where can I see a map of Mike Bost's district?
The boundary map for Illinois's 12th Congressional District is on this page. It is drawn from U.S. Census Bureau TIGERweb boundary files for the 119th Congress.
What committees is Mike Bost on?
Mike Bost sits on House Committee on Transportation and Infrastructure, House Committee on Agriculture and House Committee on Veterans' Affairs. Committee assignments come from the Clerk of the House MemberData file.
Is Mike Bost still in Congress?
This site shows Mike Bost holding Illinois's 12th Congressional District, checked against the Clerk of the House member list. All 435 House seats are on the ballot on November 3, 2026, so the answer can change with that election.
Nearby Districts in Illinois
ZIP Codes in Illinois's 12th Congressional District
This congressional district contains 291 ZIP codes. The most common 10 are shown below; expand the full list to see every ZIP in the district.
50 of these ZIP codes also extend into another Illinois district, so a ZIP code here does not always identify a single representative. Examples include 61910 (also in the 15th), 61911 (also in the 15th), 61912 (also in the 15th), 61920 (also in the 15th), 61928 (also in the 15th), 61930 (also in the 15th), 61931 (also in the 15th), 61933 (also in the 15th).
- 61910
- 61911
- 61912
- 61920
- 61928
- 61930
- 61931
- 61933
- 61938
- 61943
View all 291 ZIP codes in this district
- 61910
- 61911
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- 63673
ZIP-to-district boundaries sourced from the U.S. Census Bureau's 2024-07-30 Block Equivalency File for the 119th Congress. ZCTAs (ZIP Code Tabulation Areas) approximate USPS delivery ZIPs.
U.S. Senators for this state: Richard J. Durbin (D), Tammy Duckworth (D)
Last updated September 27, 2026.
Data last checked September 26, 2026.
See how this district compares with another using Compare Districts.