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| Aggregate | ||||||
| Counties | 1875 | 1870 | 1860 | 1850 | 1846 | Voters |
| Adair | 7045 | 3982 | 984 | 1616 | ||
| Adams | 7832 | 4614 | 1533 | 1727 | ||
| Allamakee | 19158 | 17868 | 12237 | 777 | 3653 | |
| Appanoose | 2370 | 16456 | 11931 | 3131 | 527 | |
| Audubon | 17405 | 1212 | 454 | 3679 | ||
| Benton | 28807 | 22454 | 8496 | 672 | 478 | |
| Black Hawk | 22913 | 21706 | 8244 | 135 | 4877 | |
| Boone | 17251 | 14584 | 4232 | 735 | 3515 | |
| Bremer | 13220 | 12528 | 4915 | 2656 | ||
| Buchanan | 17315 | 17034 | 7906 | 517 | 3890 | |
| Buena Vista | 3561 | 1585 | 57 | 817 | ||
| Buncombe* | ||||||
| Butler | 11734 | 9951 | 3724 | 2598 | ||
| Calhoun | 3185 | 1602 | 147 | 681 | ||
| Carroll | 5760 | 2451 | 281 | 1197 | ||
| Cass | 10552 | 5464 | 1612 | 2422 | ||
| Cedar | 17879 | 19731 | 12949 | 3941 | 1253 | 3934 |
| Cerro Gordo | 6685 | 4722 | 940 | 1526 | ||
| Cherokee | 4249 | 1967 | 58 | 1001 | ||
| Chickasaw | 11400 | 10180 | 4336 | 2392 | ||
| Clarke | 10118 | 8735 | 5427 | 79 | 2213 | |
| Clay | 3559 | 1523 | 52 | 868 | ||
| Clayton | 27184 | 27771 | 20728 | 3873 | 1101 | 5272 |
| Clinton | 34295 | 35357 | 18938 | 2822 | 821 | 5569 |
| Crawford | 6039 | 2530 | 383 | 1244 | ||
| Dallas | 14386 | 12019 | 5244 | 854 | 3170 | |
| Davis | 15757 | 15565 | 13764 | 7264 | 3448 | |
| Decatur | 13249 | 12018 | 8677 | 965 | 2882 | |
| Delaware | 16893 | 17432 | 11024 | 1759 | 168 | 3662 |
| Des Moines | 35415 | 27256 | 19611 | 12988 | 5577 | 6654 |
| Dickinson | 1748 | 1389 | 180 | 394 | ||
| Dubuque | 43845 | 38969 | 31164 | 10841 | 3059 | 8759 |
| Emmett | 1436 | 1392 | 105 | 299 | ||
| Fayette | 20515 | 16973 | 12073 | 825 | 4637 | |
| Floyd | 13100 | 10768 | 3744 | 2884 | ||
| Franklin | 6558 | 4738 | 1309 | 1374 | ||
| Fremont | 13719 | 11173 | 5074 | 1244 | 2998 | |
| Greene | 7028 | 4627 | 1374 | 1622 | ||
| Grundy | 8134 | 6399 | 793 | 1525 | ||
| Guthrie | 9638 | 7061 | 3058 | 2339 | ||
| Hamilton | 7701 | 6055 | 1699 | 1455 | ||
| Hancock | 1482 | 999 | 179 | 303 | ||
| Hardin | 15029 | 13684 | 5440 | 3215 | ||
| Harrison | 11818 | 8931 | 3621 | 2658 | ||
| Henry | 21594 | 21463 | 18701 | 8707 | 3772 | 4641 |
| Howard | 7875 | 6282 | 3168 | 1712 | ||
| Humboldt | 3455 | 2596 | 332 | 695 | ||
| Ida | 794 | 226 | 43 | 172 | ||
| Iowa | 17456 | 16644 | 8029 | 822 | 3576 | |
| Jackson | 23061 | 22619 | 18493 | 7210 | 1411 | 4901 |
| Jasper | 24128 | 22116 | 9883 | 1280 | 5239 | |
| Jefferson | 17127 | 17839 | 15038 | 9904 | 2773 | 3721 |
| Johnson | 24654 | 24898 | 17573 | 4472 | 1491 | 5225 |
| Jones | 19168 | 19731 | 13306 | 3307 | 471 | 4180 |
| Keokuk | 20488 | 19434 | 13271 | 4822 | 4202 | |
| Kossuth | 3765 | 3351 | 416 | 773 | ||
| Lee | 33913 | 38210 | 29232 | 18861 | 6093 | 5709 |
| Linn | 31815 | 28852 | 18947 | 5444 | 1373 | 7274 |
| Louisa | 12499 | 12877 | 10370 | 4939 | 1927 | 2899 |
| Lucas | 11725 | 10388 | 5766 | 471 | 2464 | |
| Lyon* | 1139 | 221 | 287 | |||
| Madison | 16030 | 13884 | 7339 | 1179 | 2632 | |
| Mahaska | 23718 | 22508 | 14816 | 5989 | 5287 | |
| Marion | 24094 | 24436 | 16813 | 5482 | 4988 | |
| Marshall | 19629 | 17576 | 6015 | 338 | 4445 | |
| Mills | 10555 | 8718 | 4481 | 2365 | ||
| Mitchell | 11523 | 9582 | 3409 | 2338 | ||
| Monona | 2267 | 3654 | 832 | 1292 | ||
| Monroe | 12811 | 12724 | 8612 | 2884 | 2743 | |
| Montgomery | 10389 | 5934 | 1256 | 2485 | ||
| Muscatine | 21623 | 21688 | 16444 | 5731 | 1942 | 6588 |
| O'Brien | 2349 | 715 | 8 | 595 | ||
| Osceola | 1778 | 498 | ||||
| Page | 14274 | 9975 | 4419 | 551 | 3222 | |
| Palo Alto | 2728 | 1336 | 132 | 556 | ||
| Plymouth | 5282 | 2199 | 148 | 1136 | ||
| Pocahontas | 2249 | 1446 | 103 | 464 | ||
| Polk | 31558 | 27857 | 11625 | 4513 | 6842 | |
| Pottawattomie | 21665 | 16893 | 4968 | 7828 | 4392 | |
| Poweshiek | 16482 | 15581 | 5668 | 615 | 3634 | |
| Ringgold | 7546 | 5691 | 2923 | 1496 | ||
| Sac | 2873 | 1411 | 246 | 657 | ||
| Scott | 39763 | 38599 | 25959 | 5986 | 2140 | 7109 |
| Shelby | 5664 | 2540 | 818 | 1084 | ||
| Sioux | 3720 | 576 | 10 | 637 | ||
| Story | 13111 | 11651 | 4051 | 2574 | ||
| Tama | 18771 | 16131 | 5285 | 8 | 3911 | |
| Taylor | 10418 | 6989 | 3590 | 204 | 2282 | |
| Union | 8827 | 6986 | 2012 | 1924 | ||
| Van Buren | 17980 | 17672 | 17081 | 12270 | 6146 | 3893 |
| Wapello | 18541 | 22346 | 14518 | 8471 | 3923 | |
| Warren | 19269 | 17980 | 10281 | 961 | 4168 | |
| Washington | 23865 | 18952 | 14235 | 4957 | 1594 | 5346 |
| Wayne | 13978 | 11287 | 6409 | 340 | 2947 | |
| Webster | 13114 | 10484 | 2504 | 3747 | ||
| Winnebago | 24233 | 1562 | 168 | 4117 | ||
| Winneshiek | 2986 | 23570 | 13942 | 546 | 406 | |
| Woodbury | 8586 | 6172 | 1119 | 1776 | ||
| Worth | 4908 | 2892 | 756 | 763 | ||
| Wright | 3244 | 2392 | 653 | 694 | ||
| Total | 1353118 | 1191792 | 674913 | 192214 | 43112 | 284557 |
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