Westmoreland County is a
county located in the
U.S. state of
Pennsylvania. As of 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, an historic county of
England.