| County | FIPS Code | County Seat | Established in | Population | Area (sq mi) | Area (km2) |
|---|---|---|---|---|---|---|
| Adams County | 1 | Friendship | 1848 | 20,875 | 645.65 | 1,672 |
| Ashland County | 3 | Ashland | 1860 | 16,157 | 1,045.04 | 2,707 |
| Barron County | 5 | Barron | 1859 | 45,870 | 862.71 | 2,234 |
| Bayfield County | 7 | Washburn | 1845 | 15,014 | 1,477.86 | 3,828 |
| Brown County | 9 | Green Bay | 1818 | 248,007 | 529.71 | 1,372 |
| Buffalo County | 11 | Alma | 1853 | 13,587 | 671.64 | 1,740 |
| Burnett County | 13 | Siren | 1856 | 15,457 | 821.85 | 2,129 |
| Calumet County | 15 | Chilton | 1836 | 48,971 | 318.24 | 824 |
| Chippewa County | 17 | Chippewa Falls | 1845 | 62,415 | 1,008.37 | 2,612 |
| Clark County | 19 | Neillsville | 1853 | 34,690 | 1,209.82 | 3,133 |
| Columbia County | 21 | Portage | 1846 | 56,833 | 765.53 | 1,983 |
| Crawford County | 23 | Prairie du Chien | 1818 | 16,644 | 570.66 | 1,478 |
| Dane County | 25 | Madison | 1836 | 488,073 | 1,197.24 | 3,101 |
| Dodge County | 27 | Juneau | 1836 | 88,759 | 875.63 | 2,268 |
| Door County | 29 | Sturgeon Bay | 1851 | 27,785 | 481.98 | 1,248 |
| Douglas County | 31 | Superior | 1854 | 44,159 | 1,304.14 | 3,378 |
| Dunn County | 33 | Menomonie | 1854 | 43,857 | 850.11 | 2,202 |
| Eau Claire County | 35 | Eau Claire | 1856 | 98,736 | 637.98 | 1,652 |
| Florence County | 37 | Florence | 1881 | 4,423 | 488.2 | 1,264 |
| Fond du Lac County | 39 | Fond du Lac | 1836 | 101,633 | 719.55 | 1,864 |
| Forest County | 41 | Crandon | 1885 | 9,304 | 1,014.07 | 2,626 |
| Grant County | 43 | Lancaster | 1837 | 51,208 | 1,146.85 | 2,970 |
| Green County | 45 | Monroe | 1837 | 36,842 | 583.96 | 1,512 |
| Green Lake County | 47 | Green Lake | 1858 | 19,051 | 349.44 | 905 |
| Iowa County | 49 | Dodgeville | 1829 | 23,687 | 762.58 | 1,975 |
| Iron County | 51 | Hurley | 1893 | 5,916 | 758.17 | 1,964 |
| Jackson County | 53 | Black River Falls | 1853 | 20,449 | 987.72 | 2,558 |
| Jefferson County | 55 | Jefferson | 1836 | 83,686 | 556.47 | 1,441 |
| Juneau County | 57 | Mauston | 1856 | 26,664 | 766.93 | 1,986 |
| Kenosha County | 59 | Kenosha | 1850 | 166,426 | 271.99 | 704 |
| Kewaunee County | 61 | Kewaunee | 1852 | 20,574 | 342.52 | 887 |
| La Crosse County | 63 | La Crosse | 1851 | 114,638 | 451.69 | 1,170 |
| Lafayette County | 65 | Darlington | 1846 | 16,836 | 633.59 | 1,641 |
| Langlade County | 67 | Antigo | 1879 | 19,977 | 870.64 | 2,255 |
| Lincoln County | 69 | Merrill | 1874 | 28,743 | 878.97 | 2,277 |
| Manitowoc County | 71 | Manitowoc | 1836 | 81,442 | 589.08 | 1,526 |
| Marathon County | 73 | Wausau | 1850 | 134,063 | 1,544.98 | 4,001 |
| Marinette County | 75 | Marinette | 1879 | 41,749 | 1,399.35 | 3,624 |
| Marquette County | 77 | Montello | 1836 | 15,404 | 455.6 | 1,180 |
| Menominee County | 78 | Keshena | 1959 | 4,232 | 357.61 | 926 |
| Milwaukee County | 79 | Milwaukee | 1834 | 947,735 | 241.4 | 625 |
| Monroe County | 81 | Sparta | 1854 | 44,673 | 900.78 | 2,333 |
| Oconto County | 83 | Oconto | 1851 | 37,660 | 997.99 | 2,585 |
| Oneida County | 85 | Rhinelander | 1885 | 35,998 | 1,112.97 | 2,883 |
| Outagamie County | 87 | Appleton | 1851 | 176,695 | 637.52 | 1,651 |
| Ozaukee County | 89 | Port Washington | 1853 | 86,395 | 233.08 | 604 |
| Pepin County | 91 | Durand | 1858 | 7,469 | 231.98 | 601 |
| Pierce County | 93 | Ellsworth | 1853 | 41,019 | 573.75 | 1,486 |
| Polk County | 95 | Balsam Lake | 1853 | 44,205 | 913.96 | 2,367 |
| Portage County | 97 | Stevens Point | 1836 | 70,019 | 800.68 | 2,074 |
| Price County | 99 | Phillips | 1879 | 14,159 | 1,254.38 | 3,249 |
| Racine County | 101 | Racine | 1836 | 195,408 | 332.5 | 861 |
| Richland County | 103 | Richland Center | 1842 | 18,021 | 586.15 | 1,518 |
| Rock County | 105 | Janesville | 1836 | 160,331 | 718.14 | 1,860 |
| Rusk County | 107 | Ladysmith | 1901 | 14,755 | 913.59 | 2,366 |
| Sauk County | 111 | Baraboo | 1840 | 61,976 | 830.9 | 2,152 |
| Sawyer County | 113 | Hayward | 1883 | 16,557 | 1,257.31 | 3,256 |
| Shawano County | 115 | Shawano | 1853 | 41,949 | 893.06 | 2,313 |
| Sheboygan County | 117 | Sheboygan | 1836 | 115,507 | 511.27 | 1,324 |
| St. Croix County | 109 | Hudson | 1840 | 84,345 | 722.33 | 1,871 |
| Taylor County | 119 | Medford | 1875 | 20,689 | 974.88 | 2,525 |
| Trempealeau County | 121 | Whitehall | 1854 | 28,816 | 732.97 | 1,898 |
| Vernon County | 123 | Viroqua | 1851 | 29,773 | 791.58 | 2,050 |
| Vilas County | 125 | Eagle River | 1893 | 21,430 | 856.6 | 2,219 |
| Walworth County | 127 | Elkhorn | 1836 | 102,228 | 555.13 | 1,438 |
| Washburn County | 129 | Shell Lake | 1883 | 15,911 | 797.11 | 2,065 |
| Washington County | 131 | West Bend | 1836 | 131,887 | 430.7 | 1,116 |
| Waukesha County | 133 | Waukesha | 1846 | 389,891 | 549.57 | 1,423 |
| Waupaca County | 135 | Waupaca | 1851 | 52,410 | 747.71 | 1,937 |
| Waushara County | 137 | Wautoma | 1851 | 24,496 | 626.15 | 1,622 |
| Winnebago County | 139 | Oshkosh | 1840 | 166,994 | 434.49 | 1,125 |
| Wood County | 141 | Wisconsin Rapids | 1856 | 74,749 | 793.12 | 2,054 |
