| Active voter registration numbers as of November 2012
IA-01
| County |
Democrats |
Republicans |
no-party voters |
| Allamakee | 2,213 | 4,326 | 3,126 |
| Benton | 4,773 | 5,105 | 7,385 |
| Black Hawk | 28,643 | 20,551 | 30,759 |
| Bremer | 3,913 | 5,128 | 7,183 |
| Buchanan | 3,957 | 3,231 | 6,333 |
| Clayton | 3,384 | 3,241 | 4,652 |
| Delaware | 2,603 | 3,832 | 4,716 |
| Dubuque | 24,768 | 14,682 | 21,783 |
| Fayette | 3,787 | 4,142 | 4,099 |
| Howard | 1,966 | 1,482 | 2,565 |
| Iowa | 2,852 | 3,768 | 4,796 |
| Jackson | 5,934 | 2,725 | 5,618 |
| Jones | 3,591 | 3,703 | 5,803 |
| Linn | 49,485 | 38,557 | 50,550 |
| Marshall | 7,840 | 7,933 | 9,239 |
| Mitchell | 1,829 | 2,560 | 2,718 |
| Poweshiek | 3,865 | 3,756 | 4,984 |
| Tama | 3,315 | 3,453 | 4,341 |
| Winnishiek | 3,589 | 4,498 | 4,982 |
| Worth | 1,594 | 1,808 | 2,027 |
| |
| total | 163,901 | 138,481 | 187,659 |
IA-02
| County |
Democrats |
Republicans |
no-party voters |
| Appanoose | 2,776 | 2,953 | 3,125 |
| Cedar | 3,230 | 3,684 | 4,570 |
| Clarke | 1,682 | 1,827 | 2,260 |
| Clinton | 11,276 | 7,400 | 13,055 |
| Davis | 1,933 | 1,545 | 1,429 |
| Decatur | 1,794 | 1,807 | 1,869 |
| Des Moines | 11,730 | 6,199 | 8,371 |
| Henry | 3,086 | 5,407 | 4,980 |
| Jasper | 8,974 | 7,258 | 7,663 |
| Jefferson | 3,476 | 3,617 | 3,441 |
| Johnson | 39,967 | 18,801 | 31,471 |
| Keokuk | 2,373 | 2,320 | 2,331 |
| Lee | 10,125 | 4,384 | 8,269 |
| Louisa | 1,887 | 2,508 | 2,606 |
| Lucas | 1,459 | 2,118 | 2,068 |
| Mahaska | 3,207 | 5,946 | 4,962 |
| Marion | 5,578 | 9,182 | 7,312 |
| Monroe | 1,799 | 1,514 | 1,504 |
| Muscatine | 7,895 | 8,327 | 10,539 |
| Scott | 35,239 | 30,334 | 44,505 |
| Van Buren | 1,094 | 2,213 | 1,631 |
| Wapello | 9,654 | 5,352 | 7,032 |
| Washington | 3,041 | 5,810 | 4,905 |
| Wayne | 1,046 | 1,384 | 1,155 |
| |
| total | 174,321 | 141,890 | 181,053 |
IA-03
| County |
Democrats |
Republicans |
no-party voters |
| Adair | 1,142 | 2,018 | 1,991 |
| Adams | 690 | 956 | 1,164 |
| Cass | 1,656 | 4,906 | 3,065 |
| Dallas | 10,402 | 16,332 | 16,764 |
| Fremont | 1,339 | 2,203 | 1,862 |
| Guthrie | 2,043 | 2,769 | 2,823 |
| Madison | 3,045 | 4,017 | 3,788 |
| Mills | 1,947 | 4,791 | 3,124 |
| Montgomery | 1,077 | 3,932 | 1,966 |
| Page | 1,697 | 4,451 | 3,600 |
| Polk | 102,979 | 82,240 | 77,249 |
| Pottawattamie | 16,412 | 21,174 | 18,098 |
| Ringgold | 911 | 1,474 | 745 |
| Taylor | 833 | 1,999 | 1,342 |
| Union | 1,791 | 2,854 | 2,981 |
| Warren | 9,940 | 10,643 | 10,427 |
| |
| total | 157,904 | 166,759 | 150,989 |
IA-04
| County |
Democrats |
Republicans |
no-party voters |
| Audubon | 1,326 | 1,610 | 1,394 |
| Boone | 5,465 | 5,628 | 6,614 |
| Buena Vista | 2,909 | 3,957 | 4,605 |
| Butler | 1,771 | 4,601 | 3,212 |
| Calhoun | 1,468 | 2,391 | 2,714 |
| Carroll | 4,232 | 4,026 | 6,290 |
| Cerro Gordo | 9,781 | 8,135 | 12,630 |
| Cherokee | 2,070 | 3,238 | 3,231 |
| Chickasaw | 2,988 | 2,214 | 3,669 |
| Clay | 2,652 | 4,580 | 4,417 |
| Crawford | 2,788 | 3,143 | 3,453 |
| Dickinson | 2,676 | 5,232 | 4,638 |
| Emmet | 2,230 | 1,716 | 3,134 |
| Floyd | 3,152 | 2,735 | 4,651 |
| Franklin | 1,313 | 3,095 | 2,248 |
| Greene | 2,059 | 2,147 | 2,308 |
| Grundy | 1,494 | 4,118 | 3,020 |
| Hamilton | 2,813 | 3,602 | 3,720 |
| Hancock | 1,614 | 3,301 | 2,932 |
| Hardin | 2,774 | 4,670 | 3,957 |
| Harrison | 2,531 | 3,590 | 2,516 |
| Humboldt | 1,388 | 2,500 | 2,509 |
| Ida | 967 | 2,173 | 1,920 |
| Kossuth | 3,544 | 3,442 | 4,161 |
| Lyon | 907 | 5,443 | 1,705 |
| Monona | 2,124 | 1,915 | 2,452 |
| O'Brien | 1,390 | 5,284 | 2,791 |
| Osceola | 533 | 2,596 | 1,086 |
| Palo Alto | 2,436 | 1,604 | 2,216 |
| Plymouth | 3,399 | 7,979 | 5,817 |
| Pocahontas | 1,146 | 1,723 | 2,227 |
| Sac | 1,391 | 3,115 | 2,596 |
| Shelby | 2,122 | 3,742 | 2,953 |
| Sioux | 1,635 | 14,478 | 3,639 |
| Story | 17,088 | 15,815 | 20,393 |
| Webster | 8,972 | 6,876 | 8,641 |
| Winnebago | 1,588 | 3,045 | 2,622 |
| Woodbury | 19,231 | 19,310 | 19,136 |
| Wright | 1,950 | 3,544 | 2,640 |
| |
| total | 131,917 | 182,313 | 174,857 |
|