In 1817 the U.S. government built Forts Howard at Green Bay, Crawford at Prairie du Chien, and Winnebago at Portage to protect settlers in what is now Wisconsin. Congress granted territorial status to Wisconsin in 1836 after a "lead rush" to the southwestern corner of the area. Belmont, in Lafayette County, was chosen as territorial capital by the territorial governor, Henry Dodge. Some political maneuvering, including bribes, caused the capital to be moved to what is now Madison.

A second influx of immigrants took place from 1840 to 1850, mostly into eastern Wisconsin. Several referendums for statehood failed locally and voters finally elected to petition Congress in 1846. Two years later President James K. Polk signed the statehood bill. During the 1850s, Wisconsin's population swelled to more than 700,000, with an influx of more than 300,000. More than 45 percent of the immigrants were from Germany. When the Civil War broke out, many residents did not feel strongly about the Union cause. After the mid-1870s, some farmers turned to dairying, at first concentrating on butter. Later the emphasis changed to cheese, which spoils less easily than butter.