The 3rd Congressional District of Illinois includes part of Cook County, and has been represented by Democrat Dan Lipinski since January 2005; the district was previously represented by his father Bill Lipinski beginning in 1993. This district includes west and southwest suburbs of Chicago as far as the DuPage County border, as well as a portion of the southwest side of the city of Chicago itself, and covers 124.5 square miles (322.45 km²), making it one of the 50 smallest districts in the U.S., although there are five smaller districts in Illinois. It is adjacent to the 1st District to the east and south, the 4th District to the north, and the 13th District to the west, and also borders the 6th and 7th Districts at its northwest and northeast corners respectively. The district was created following the 1830 Census and came into being in 1833, five months before Chicago was organized as a town; it initially included northern and western Illinois before representing areas of east central and northwestern Illinois from 1843 to 1873. The district has included part of Chicago since 1873, and part of the city's southwest side since 1895; the district has been primarily suburban since 1973.
Although the district has elected Democrats to Congress in 24 of the last 25 elections, and has voted for the Democratic nominee in the last four presidential races, there is also a strong tradition of social conservatism in the area which has resulted in the election of conservative Democrats, as well as greater support for Republicans than might be expected based on voter identification by party.