| Active voter registration numbers as of October 2012
IA-01
| County |
Democrats |
Republicans |
no-party voters |
| Allamakee | 2,190 | 4,326 | 3,078 |
| Benton | 4,732 | 5,082 | 7,327 |
| Black Hawk | 27,406 | 20,178 | 29,447 |
| Bremer | 3,743 | 5,038 | 7,064 |
| Buchanan | 3,940 | 3,221 | 6,227 |
| Clayton | 3,330 | 3,210 | 4,575 |
| Delaware | 2,565 | 3,836 | 4,691 |
| Dubuque | 24,032 | 14,302 | 21,042 |
| Fayette | 3,721 | 4,098 | 3,995 |
| Howard | 1,956 | 1,479 | 2,537 |
| Iowa | 2,810 | 3,731 | 4,751 |
| Jackson | 5,928 | 2,708 | 5,586 |
| Jones | 3,553 | 3,675 | 5,705 |
| Linn | 48,314 | 38,216 | 49,268 |
| Marshall | 7,626 | 7,900 | 9,086 |
| Mitchell | 1,822 | 2,561 | 2,669 |
| Poweshiek | 3,727 | 3,741 | 4,808 |
| Tama | 3,248 | 3,440 | 4,256 |
| Winnishiek | 3,403 | 4,416 | 4,635 |
| Worth | 1,596 | 1,797 | 1,995 |
| |
| total | 159,642 | 136,955 | 182,742 |
IA-02
| County |
Democrats |
Republicans |
no-party voters |
| Appanoose | 2,739 | 2,935 | 3,038 |
| Cedar | 3,152 | 3,656 | 4,494 |
| Clarke | 1,647 | 1,819 | 2,204 |
| Clinton | 11,012 | 7,358 | 12,815 |
| Davis | 1,949 | 1,526 | 1,398 |
| Decatur | 1,740 | 1,789 | 1,793 |
| Des Moines | 11,436 | 6,129 | 8,132 |
| Henry | 3,008 | 5,389 | 4,859 |
| Jasper | 8,799 | 7,192 | 7,435 |
| Jefferson | 3,285 | 3,579 | 3,371 |
| Johnson | 38,212 | 17,996 | 29,127 |
| Keokuk | 2,341 | 2,332 | 2,246 |
| Lee | 10,017 | 4,353 | 8,071 |
| Louisa | 1,841 | 2,508 | 2,575 |
| Lucas | 1,426 | 2,109 | 2,033 |
| Mahaska | 3,067 | 5,872 | 4,810 |
| Marion | 5,505 | 9,100 | 7,026 |
| Monroe | 1,774 | 1,498 | 1,462 |
| Muscatine | 7,727 | 8,271 | 10,333 |
| Scott | 34,028 | 29,960 | 43,530 |
| Van Buren | 1,081 | 2,210 | 1,622 |
| Wapello | 9,538 | 5,316 | 6,788 |
| Washington | 2,969 | 5,797 | 4,770 |
| Wayne | 1,022 | 1,369 | 1,115 |
| |
| total | 169,315 | 140,063 | 175,047 |
IA-03
| County |
Democrats |
Republicans |
no-party voters |
| Adair | 1,130 | 2,018 | 1,951 |
| Adams | 694 | 950 | 1,145 |
| Cass | 1,631 | 4,897 | 3,028 |
| Dallas | 9,935 | 15,927 | 16,256 |
| Fremont | 1,332 | 2,198 | 1,840 |
| Guthrie | 2,036 | 2,755 | 2,786 |
| Madison | 3,031 | 3,979 | 3,732 |
| Mills | 1,914 | 4,756 | 3,046 |
| Montgomery | 1,064 | 3,929 | 1,904 |
| Page | 1,658 | 4,417 | 3,523 |
| Polk | 99,659 | 81,054 | 74,471 |
| Pottawattamie | 16,018 | 20,945 | 17,524 |
| Ringgold | 903 | 1,463 | 720 |
| Taylor | 813 | 1,997 | 1,330 |
| Union | 1,757 | 2,834 | 2,897 |
| Warren | 9,782 | 10,527 | 10,115 |
| |
| total | 153,357 | 164,646 | 146,268 |
IA-04
| County |
Democrats |
Republicans |
no-party voters |
| Audubon | 1,321 | 1,602 | 1,379 |
| Boone | 5,359 | 5,588 | 6,502 |
| Buena Vista | 2,840 | 3,937 | 4,466 |
| Butler | 1,729 | 4,583 | 3,159 |
| Calhoun | 1,444 | 2,381 | 2,691 |
| Carroll | 4,207 | 4,008 | 6,244 |
| Cerro Gordo | 9,666 | 8,100 | 12,458 |
| Cherokee | 2,043 | 3,193 | 3,223 |
| Chickasaw | 2,994 | 2,211 | 3,629 |
| Clay | 2,624 | 4,562 | 4,335 |
| Crawford | 2,704 | 3,110 | 3,405 |
| Dickinson | 2,623 | 5,157 | 4,530 |
| Emmet | 2,220 | 1,702 | 3,116 |
| Floyd | 3,103 | 2,731 | 4,559 |
| Franklin | 1,258 | 3,086 | 2,245 |
| Greene | 2,047 | 2,147 | 2,261 |
| Grundy | 1,471 | 4,111 | 2,976 |
| Hamilton | 2,768 | 3,586 | 3,682 |
| Hancock | 1,601 | 3,298 | 2,915 |
| Hardin | 2,680 | 4,644 | 3,877 |
| Harrison | 2,471 | 3,499 | 2,414 |
| Humboldt | 1,375 | 2,503 | 2,451 |
| Ida | 968 | 2,163 | 1,907 |
| Kossuth | 3,529 | 3,418 | 4,128 |
| Lyon | 904 | 5,398 | 1,675 |
| Monona | 2,105 | 1,898 | 2,413 |
| O'Brien | 1,371 | 5,271 | 2,755 |
| Osceola | 523 | 2,596 | 1,068 |
| Palo Alto | 2,431 | 1,582 | 2,151 |
| Plymouth | 3,345 | 7,941 | 5,722 |
| Pocahontas | 1,124 | 1,725 | 2,189 |
| Sac | 1,379 | 3,092 | 2,557 |
| Shelby | 2,083 | 3,735 | 2,877 |
| Sioux | 1,602 | 14,332 | 3,550 |
| Story | 16,174 | 15,248 | 19,186 |
| Webster | 8,814 | 6,851 | 8,419 |
| Winnebago | 1,577 | 3,043 | 2,588 |
| Woodbury | 18,569 | 18,954 | 18,808 |
| Wright | 1,924 | 3,526 | 2,604 |
| |
| total | 128,970 | 180,512 | 171,114 |
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