Wisconsin's 4th congressional district is a congressional district of the United States House of Representatives in Wisconsin, encompassing a part of Milwaukee County and including almost all of the city of Milwaukee, as well as its working-class suburbs of Cudahy, St. Francis, South Milwaukee, and West Milwaukee. Recent redistricting has added the Milwaukee County North Shore communities of Glendale, Shorewood, Whitefish Bay, Fox Point, Bayside, and Brown Deer to the district. It is currently represented by Gwen Moore, a Democrat.

Milwaukee County is located in the U.S. state of Wisconsin. At the 2020 census, the population was 939,489, down from 947,735 in 2010. It is both the most populous and most densely populated county in Wisconsin, and the 45th most populous county nationwide; Milwaukee, its eponymous county seat, is also the most populous city in the state. The county was created in 1834 as part of Michigan Territory and organized the following year.