Wilmerding is a borough in Allegheny County, Pennsylvania, United States. The population was 2,145 at the 2000 census. It is located 12 miles (19 km) southeast of Pittsburgh. At the start of the twentieth century, it had extensive foundries and machine shops of the Westinghouse Air Brake Company. In 1900, the population stood at 4,179 people; in 1910, it stood at 6,133. 5,662 residents were counted in 1940. Wilmerding is adjacent to Turtle Creek, which takes its name from a small stream that flows past both places.
George Westinghouse purchased land in the Turtle Creek Valley in 1887 and 1888 as a site for his Westinghouse Air Brake Company and related facilities. Westinghouse then sold the land to the East Pittsburgh Improvement Company, incorporated in December 1888, to develop the site, and it began the sale of lots in June 1889.
Wilmerding's most notable historic structure is the Westinghouse Air Brake Company General Office Building (1889–1890, rebuilt 1896), designed by Frederick J. Osterling and now listed on the National Register of Historic Places.