In Washington county, the city of Washington and eastern portions of the county, a large and Democratic edge suburb of Pittsburgh, was a part of the 12th. Most of the Monongahela Valley region, a very Democratic area once an important steel-making area, was also part of the 12th.
The geographic area encompassing Washington County, including the city of Washington and the Monongahela Valley, was represented by the 12th congressional district. This district had a strong Democratic presence due to its location in an historically Democratic region with a significant steel industry.