Wisconsin had become a state only five years before Sjoerd arrived. It was the last state east of the Mississippi to gain statehood, on May 29, 1848.
In 1850 the population was about 300,000, with about a third of the population born in New England, 20% born in Wisconsin, and most of the rest immigrants.
Here is an 1855 map of the La Crosse and Milwaukee Rail Road (and connections!). This Mississippi wasn’t the only way to get there.
Here is a state map of Wisconsin from 1855. New Amsterdam represented!
Source of both maps: Library of Congress