[5] At the time of the creation of the state of Wisconsin, the 4th Senate District was defined in the Constitution as consisting of Fond du Lac and Winnebago counties.

The new 4th was represented by: For the 1857 session, the Senate was expanded to 30 seats; the new 4th district included all of Washington County now, and once more elected: As of 1862, the Senate expanded to 33 seats, a size it would retain well into the 21st century; the 4th District remained unchanged.

The new 4th encompassed the seven North Shore suburbs, but also Thiensville, Mequon, and eight townships in Southeastern Washington County, from Erin in the southwest to Farmington in the northeast.

A 1992 court-ordered redistricting moved most of the district west of the Milwaukee River, except for Glendale and part of Shorewood, and added a large slice of the inner city, extending at its westmost to the county line with Waukesha County.

This new 4th elected: A new court-ordered map was created in 2002, by which the District was moved even further west into the inner city and out to 124th Street.

The 2011 redistricting expanded the portion of the district in the inner city, while still retaining Shorewood and part of Glendale.

Previous politicians of a specific numbered district have represented a completely different geographic area, due to redistricting.