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.

Greater Pittsburgh is the metropolitan area surrounding the city of Pittsburgh in Western Pennsylvania, United States. The region includes Allegheny County, Pittsburgh's urban core county and economic hub, and seven adjacent Pennsylvania counties: Armstrong, Beaver, Butler, Fayette, Lawrence, Washington, and Westmoreland in Western Pennsylvania, which constitutes the Pittsburgh, PA Metropolitan Statistical Area MSA as defined by the U.S. Census Bureau.