40.1  Congressional districts.
  The state of Iowa is hereby organized and divided into four congressional districts, which shall be composed, respectively, of the following counties:
  1.  The first district shall consist of the counties of Worth, Mitchell, Howard, Winneshiek, Allamakee, Bremer, Fayette, Clayton, Black Hawk, Buchanan, Delaware, Dubuque, Marshall, Tama, Benton, Linn, Jones, Jackson, Poweshiek, and Iowa.
  2.  The second district shall consist of the counties of Jasper, Johnson, Cedar, Clinton, Marion, Mahaska, Keokuk, Washington, Louisa, Muscatine, Scott, Clarke, Lucas, Monroe, Wapello, Jefferson, Henry, Des Moines, Decatur, Wayne, Appanoose, Davis, Van Buren, and Lee.
  3.  The third district shall consist of the counties of Guthrie, Dallas, Polk, Pottawattamie, Cass, Adair, Madison, Warren, Mills, Montgomery, Adams, Union, Fremont, Page, Taylor, and Ringgold.
  4.  The fourth district shall consist of the counties of Lyon, Osceola, Dickinson, Emmet, Kossuth, Winnebago, Sioux, O’Brien, Clay, Palo Alto, Hancock, Cerro Gordo, Floyd, Chickasaw, Plymouth, Cherokee, Buena Vista, Pocahontas, Humboldt, Wright, Franklin, Butler, Woodbury, Ida, Sac, Calhoun, Webster, Hamilton, Hardin, Grundy, Monona, Crawford, Carroll, Greene, Boone, Story, Harrison, Shelby, and Audubon.
[C27, 31, 35, §526-a1; C39, §526.1; C46, 50, 54, 58, 62, 66, 71, 73, 75, 77, 79, 81, §40.1; 
81 Acts 2d Ex, ch 1, §1
]
91 Acts, ch 223, §1
; 2001 Acts, 1st Ex, ch 1, §1, 6
; 2011 Acts, ch 76, §1, 6

Constitutional provision, Iowa Constitution, Art. III, §37
Membership beginning in 2013; see 
2011 Acts, ch 76, §3, 4