Pennsylvania's 12th congressional district is located in southwestern Pennsylvania, including Pittsburgh and much of Allegheny County, as well as some of Westmoreland County. Since January 3, 2023, it has been represented by Summer Lee.

Westmoreland County is a county in the Commonwealth of Pennsylvania, United States, located in the Pittsburgh Metropolitan Statistical Area. As of the 2020 census, the population was 354,663. The county seat is Greensburg and the most populous community is Hempfield Township. It is named after Westmorland, a historic county of England. The county is part of the Southwest Pennsylvania region of the state.