[1] Located in southeast Wisconsin, the district is entirely contained within northwest Milwaukee County.

It comprises much of the far north of the city of Milwaukee as well as part of northern Wauwatosa and western Brown Deer.

The district also includes most of the former town of Granville, Dretzka Park, and Lawrence J. Timmerman Airport.

[6] The 1982 court-ordered redistricting plan moved the 12th district into central Milwaukee County.

[7] The district has remained in Milwaukee County since then, though the boundaries shifted east in the 1983 legislative redistricting, and then north and west in 1992, 2002, and 2011, with the district now covering the northwest corner of the county.