Illinois's 12th congressional district

The district covers parts of Madison and St. Clair counties, and all of Alexander, Franklin, Hamilton, Jackson, Jefferson, Monroe, Perry, Pulaski, Randolph, Union and Williamson counties, as of the 2011 redistricting which followed the 2010 census. All or parts of Belleville, Cahokia, Carbondale, Collinsville, East St. Louis, Granite City, Herrin, Marion, Mt. Vernon, O'Fallon, Shiloh and Swansea are included.^[3] The representatives for these districts were elected in the 2012 primary and general elections, and the boundaries became effective on January 5, 2013.

• Belleville – 42,404
• O'Fallon – 32,289
• Carbondale – 25,083
• Charleston – 17,286
• Mattoon – 16,870
• Marion – 16,855
• Fairview Heights – 16,706
• Mount Vernon – 14,600
• Shiloh – 14,098
• Herrin – 12,352
• Effingham – 12,252
• Centralia – 12,182
• Waterloo – 11,013
• Columbia – 10,999

• Mascoutah – 8,754
• Olney – 8,701
• Harrisburg – 8,219
• Chester – 7,640
• Salem – 7,282
• West Frankfort – 7,275
• Robinson – 7,150
• Murphysboro – 7,093
• Mount Carmel – 7,015
• Benton – 6,709
• Metropolis – 5,969
• Carterville – 5,848
• Du Quoin – 5,827
• Pinckneyville – 5,066
• Fairfield – 4,883
• Carmi – 4,865
• Flora – 4,803
• Lebanon – 4,691
• Breese – 4,641
• Freeburg – 4,582
• Caseyville – 4,400
• Anna – 4,303
• Lawrenceville – 4,164
• Sparta – 4,095
• Millstadt – 4,071
• Smithton – 4,006
• Marshall – 3,947
• Red Bud – 3,804
• Eldorado – 3,743
• Scott AFB – 3,612
• New Baden – 3,428
• Johnston City – 3,384
• Carlyle – 3,253
• Nashville – 3,105
• Newton – 2,777
• Christopher – 2,697
• Trenton – 2,690
• McLeansboro – 2,675
• Sumner – 2,631

Following the 2020 redistricting, this district will go from covering southeastern Illinois to encompassing the entirety of Southern Illinois, spanning the Illinois-Missouri-Kentucky-Indiana border. It will take in Monroe, Randolph, Clinton, Perry, Jackson, Union, Alexander, Pulaski, Massac, Johnson, Williamson, Jefferson, Marion, Clay, Effingham, Wayne, Hamilton, Saline, Pope, Hardin, Gallatin, White, Edwards, Wabash, Richland, Lawrence, Jasper, Crawford, Cumberland, and Clark Counties, most of St. Clair County, and half of Coles County.

St. Clair County is split between this district and the 13th district. They are partitioned by a Conrail line, Tanglewood Parkway, Donner Ridge, Hollywood Heights Rd, Oliver St, CSX Transportation Line, S Oak St, W 5th St, S Lincoln Ave, E US Highway 50, County Rd 218, Old O'Fallon Rd, Frank Scott Parkway E, N Green Mount Rd, S Green Mount Rd, Park Rd, S 59th St, Old St. Louis Rd, Illinois Highway 15, Rolling Acres Ln, Excellence Dr, Powdermill Creek, Cemetery Rd, and Illinois Highway 50. The 12th district takes in the municipalities of Mascoutah, Lebanon, New Athens, Marissa, Millstadt, Smithton, Freeburg, Summerfield, Scott AFB, Rentchler, Floraville, Paderborn, Fayetteville, St. Libory, Darmstadt, and Lenzburg; most of Shiloh; half of O'Fallon; and part of Caseyville, Fairview Heights, and Belleville.

Coles County is split between this district and the 15th district. They are partitioned by West St, North County Rd 1800 East, Lincoln Prairie Grass Trail, 18th St, County Rd 1600 East, County Rd 400 North, County Rd 1240 East, Illinois Route 16, Dettro Dr, 700 North Rd, Old Fellow Rd, and the Kickapoo Creek. The 12th district takes in the communities of Ashmore, Oakland, Lerna, Janesville (shared with Cumberland County), and Trilla; part of southern Mattoon; and part of Charleston.

This table indicates how the district has voted in U.S. presidential elections; election results reflect voting in the district as it was configured at the time of the election, not as it is configured today.

This table indicates how the district has voted in recent statewide elections; election results reflect voting in the district as it is currently configured, not necessarily as it was at the time of these elections.

• Illinois's congressional districts
• List of United States congressional districts

• Martis, Kenneth C. (1989). The Historical Atlas of Political Parties in the United States Congress. New York: Macmillan Publishing Company.
• Martis, Kenneth C. (1982). The Historical Atlas of United States Congressional Districts. New York: Macmillan Publishing Company.
• Congressional Biographical Directory of the United States 1774–present, bioguide.congress.gov; accessed November 10, 2016.

• Washington Post page on the 12th District of Illinois
• U.S. Census Bureau - 5th District Fact Sheet Archived September 28, 2011, at the Wayback Machine

38°00′N 89°15′W / 38.000°N 89.250°W / 38.000; -89.250