The Fourth Principal Meridian from Illinois was extended northward to what is now Wisconsin’s southern border in order to conduct the public land survey for that territory, which began at this Initial Point in 1832. In late 1831, earth was mounded up to a height of six feet here, and a post was set, to be visible by surveyors, who then proceeded north along the meridian, using 66-foot long surveyor chains to measure as they went, and placing wooden posts in the ground every half mile (every 40 chains). The original mound and post placed at the Initial Point are long gone, removed by powerline and fence crews, but a small concrete surveyors monument has been reinstalled at the site, which is on private property.
This USGS topographic map shows the north/south Fourth Meridian intersecting the east/west baseline (which is now the state line between Illinois and Wisconsin), near the center of the map.
All of Wisconsin and part of Minnesota was surveyed off Wisconsin’s Fourth Meridian (area in yellow).