There are 77 US Post Offices in Westmoreland County serving a total of 413,314 residents equating to 5,368 residents per post office. It's estimated that approximately 659,695 packages are handled across the 77 county post offices annually. Westmoreland County is a county located in the U.S. state of Pennsylvania. At the 2010 census, the population was 365,169. The county seat is Greensburg. Cut from Lancaster, Northumberland, and later Bedford Counties, Westmoreland County was founded on February 26, 1773 and was the first county in the colony of Pennsylvania in which its entire territorial boundary was located west of the Allegheny Mountains. Westmoreland County originally included the present-day counties of Fayette, Washington, Greene, and parts of Beaver, Allegheny, Indiana, and Armstrong counties. It is named for Westmorland, a historic county of England. Westmoreland County is included in the Pittsburgh, PA Metropolitan Statistical Area. A major coal strike occurred in the county in the winter of 1910\u201311."