Illinois has 102 counties and 19 congressional districts: 71 counties are wholly within a given congressional district and 31 counties are divided among more than one congressional district.
UNDIVIDED COUNTIES (wholly within one Congressional District):
- CD # 11: Grundy, Kankakee and LaSalle
- CD # 12: Alexander, Franklin, Jackson, Monroe, Perry, Pulaski, Randolph, St.Clair and Union
- CD # 14: Kane, Kendall and Lee
- CD # 15: Champaign, Clark, Coles, Crawford, Cumberland, DeWitt, Douglas, Edgar, Ford, Iroquois, Moultrie, Piatt and Vermilion
- CD # 16: Boone, Carroll, Jo Daviess, Ogle, Stephenson and Winnebago
- CD # 17: Calhoun, Fulton, Hancock, Henderson, Macoupin, McDonough, Mercer, Rock Island and Warren
- CD # 18: Brown, Cass, Logan, Marshall, Mason, Menard, Morgan, Peoria, Putnam, Schuyler, Scott, Stark and Tazewell
- CD # 19: Bond, Clay, Clinton, Effingham, Hamilton, Hardin, Jasper, Jefferson, Johnson, Marion, Massac, Pope, Richland, Washington and Wayne
DIVIDED COUNTIES (split between more than one Congressional District):
- Adams: CDs 17 & 18
- Bureau: CDs 11, 14 & 18
- Christian: CDs 19 & 17
- Cook: CDs 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 & 13 [CDs # 1, # 2, # 3, # 4, # 5, # 7 and # 9 are wholly within Cook County]
- DeKalb: CDs 14 & 16
- DuPage: CDs 6, 13 & 14
- Edwards: CDs 15 & 19
- Fayette: CDs 17 & 19
- Gallatin: CDs 15 & 19
- Greene: CDs 17 & 19
- Henry: CDs 14 & 17
- Jersey: CDs 17 & 19
- Knox: CDs 17 & 18
- Lake: CDs 8 & 10
- Lawrence: CDs 15 & 19
- Livingston: CDs 11 & 15
- Macon: CDs 15, 17 & 18
- Madison: CDs 12 & 19
- McHenry: CDs 8 & 16
- McLean: CDs 11 & 15
- Montgomery: CDs 17 & 19
- Pike: CDs 17 & 18
- Saline: CDs 15 & 19
- Sangamon: CDs 17 & 19
- Shelby: CDs 17 & 19
- Wabash: CDs 15 & 19
- White: CDs 15 & 19
- Whiteside: CDs 14, 16 & 17
- Will: CDs 11 & 13
- Williamson: CDs 12 & 19
- Woodford: CDs 11 & 18
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