The 5th congressional district of Illinois covers parts of Cook and Lake counties, as of the 2023 redistricting which followed the 2010 census. All or parts of Chicago, Inverness, Arlington Heights, Barrington Hills, Des Plaines, Palatine, Mount Prospect, Deer Park, Kildeer, Lake Zurich, Long Grove, and North Barrington are included.

Lake County is situated in the northeastern corner of the U.S. state of Illinois, along the shores of Lake Michigan. As of the 2020 census, it has a population of 714,342, making it the third-most populous county in Illinois. Its county seat is Waukegan, the tenth-largest city in Illinois. The county is primarily suburban, with some urban areas and some rural areas. Due to its location, immediately north of Cook County, Lake County is one of the collar counties of the Chicago metropolitan area. Its northern boundary is the Wisconsin state line.