| Active voter registration numbers as of May 2012
IA-01
| County |
Democrats |
Republicans |
no-party voters |
| Allamakee | 2,439 | 3,612 | 3,482 |
| Benton | 4,601 | 5,021 | 7,280 |
| Black Hawk | 26,124 | 19,617 | 27,709 |
| Bremer | 3,612 | 4,898 | 6,967 |
| Buchanan | 4,007 | 3,151 | 6,309 |
| Clayton | 3,278 | 3,183 | 4,446 |
| Delaware | 2,692 | 3,952 | 4,883 |
| Dubuque | 24,606 | 14,210 | 21,556 |
| Fayette | 3,546 | 3,982 | 4,106 |
| Howard | 1,934 | 1,485 | 2,474 |
| Iowa | 2,789 | 3,697 | 4,709 |
| Jackson | 5,982 | 2,657 | 5,328 |
| Jones | 3,601 | 3,727 | 5,711 |
| Linn | 46,289 | 38,179 | 47,733 |
| Marshall | 7,440 | 8,028 | 9,170 |
| Mitchell | 1,825 | 2,506 | 2,653 |
| Poweshiek | 3,442 | 3,670 | 4,570 |
| Tama | 3,144 | 3,432 | 4,181 |
| Winnishiek | 3,268 | 4,304 | 4,594 |
| Worth | 1,659 | 1,597 | 2,111 |
| |
| total | 156,278 | 134,908 | 179,972 |
IA-02
| County |
Democrats |
Republicans |
no-party voters |
| Appanoose | 2,727 | 2,927 | 3,011 |
| Cedar | 3,074 | 3,646 | 4,443 |
| Clarke | 1,649 | 1,809 | 2,391 |
| Clinton | 10,486 | 7,416 | 12,650 |
| Davis | 1,916 | 1,523 | 1,373 |
| Decatur | 1,742 | 1,786 | 1,773 |
| Des Moines | 11,246 | 6,082 | 7,936 |
| Henry | 3,105 | 4,780 | 5,186 |
| Jasper | 9,354 | 7,548 | 7,791 |
| Jefferson | 3,035 | 3,624 | 3,326 |
| Johnson | 35,433 | 17,767 | 27,476 |
| Keokuk | 2,300 | 2,283 | 2,314 |
| Lee | 9,744 | 4,353 | 8,146 |
| Louisa | 1,856 | 2,566 | 2,557 |
| Lucas | 1,443 | 2,063 | 2,038 |
| Mahaska | 2,980 | 5,840 | 4,687 |
| Marion | 5,559 | 8,467 | 7,055 |
| Monroe | 1,781 | 1,508 | 1,420 |
| Muscatine | 7,549 | 8,077 | 10,020 |
| Scott | 32,068 | 29,372 | 42,399 |
| Van Buren | 1,089 | 2,171 | 1,635 |
| Wapello | 9,483 | 5,235 | 6,618 |
| Washington | 2,997 | 5,315 | 4,922 |
| Wayne | 1,025 | 1,307 | 1,118 |
| |
| total | 163,641 | 137,465 | 172,285 |
IA-03
| County |
Democrats |
Republicans |
no-party voters |
| Adair | 1,135 | 2,026 | 1,935 |
| Adams | 730 | 976 | 1,161 |
| Cass | 1,619 | 4,898 | 2,958 |
| Dallas | 10,294 | 15,625 | 17,314 |
| Fremont | 1,329 | 2,165 | 1,829 |
| Guthrie | 1,997 | 2,813 | 2,730 |
| Madison | 3,023 | 3,881 | 3,669 |
| Mills | 1,927 | 4,489 | 3,123 |
| Montgomery | 1,085 | 3,685 | 2,008 |
| Page | 1,620 | 4,341 | 3,492 |
| Polk | 96,379 | 79,995 | 70,856 |
| Pottawattamie | 15,803 | 19,341 | 17,817 |
| Ringgold | 1,006 | 1,285 | 766 |
| Taylor | 912 | 1,657 | 1,474 |
| Union | 1,767 | 2,790 | 2,862 |
| Warren | 9,650 | 10,235 | 10,191 |
| |
| total | 150,276 | 160,202 | 144,185 |
IA-04
| County |
Democrats |
Republicans |
no-party voters |
| Audubon | 1,348 | 1,438 | 1,460 |
| Boone | 5,396 | 5,075 | 6,551 |
| Buena Vista | 2,789 | 3,894 | 4,405 |
| Butler | 1,765 | 4,405 | 3,207 |
| Calhoun | 1,451 | 2,280 | 2,713 |
| Carroll | 4,265 | 3,902 | 6,192 |
| Cerro Gordo | 9,555 | 8,037 | 12,241 |
| Cherokee | 2,057 | 3,160 | 3,198 |
| Chickasaw | 2,962 | 2,222 | 3,589 |
| Clay | 2,648 | 4,479 | 4,324 |
| Crawford | 2,632 | 3,018 | 3,418 |
| Dickinson | 2,797 | 4,680 | 4,913 |
| Emmet | 2,257 | 1,691 | 3,075 |
| Floyd | 3,119 | 2,708 | 4,527 |
| Franklin | 1,279 | 2,934 | 2,324 |
| Greene | 1,750 | 2,243 | 2,423 |
| Grundy | 1,505 | 3,955 | 3,073 |
| Hamilton | 2,753 | 3,617 | 3,589 |
| Hancock | 1,611 | 3,290 | 2,883 |
| Hardin | 2,761 | 4,246 | 4,090 |
| Harrison | 2,463 | 3,511 | 2,386 |
| Humboldt | 1,377 | 2,445 | 2,440 |
| Ida | 964 | 2,161 | 1,871 |
| Kossuth | 3,589 | 3,274 | 4,121 |
| Lyon | 1,000 | 5,046 | 1,824 |
| Monona | 2,108 | 1,873 | 2,385 |
| O'Brien | 1,355 | 5,137 | 2,806 |
| Osceola | 529 | 2,447 | 1,156 |
| Palo Alto | 2,166 | 1,613 | 2,267 |
| Plymouth | 3,435 | 7,637 | 5,851 |
| Pocahontas | 1,143 | 1,677 | 2,213 |
| Sac | 1,363 | 3,048 | 2,560 |
| Shelby | 2,256 | 3,205 | 3,120 |
| Sioux | 1,563 | 14,195 | 3,439 |
| Story | 16,601 | 16,040 | 20,302 |
| Webster | 8,801 | 6,771 | 8,289 |
| Winnebago | 1,653 | 2,711 | 2,714 |
| Woodbury | 18,039 | 18,094 | 18,970 |
| Wright | 1,925 | 3,362 | 2,615 |
| |
| total | 129,030 | 175,521 | 173,524 |
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