Trafford is a borough in Allegheny and Westmoreland counties in the U.S. state of Pennsylvania. Located near Pittsburgh in western Pennsylvania, the borough lies primarily in Westmoreland County; only a small portion extends into Allegheny County. It was incorporated in 1904 from the northernmost corner of North Huntingdon Township, and was named by George Westinghouse for Trafford near Manchester, England. Westinghouse purchased the land in 1902, and the Trafford Foundry began operations on October 3, 1903. The population was 3,317 at the 2020 census. Of this, 3,113 were in Westmoreland County, and only 61 were in Allegheny County.

To provide workers for the foundry, the Pennsylvania Railroad ran six passenger trains daily to Trafford from Pittsburgh. The steam locomotives of the time were manufactured to only travel forward for long distances with a limited reverse function. In order to turn the locomotives for the return trips to Pittsburgh a "wye" (Y) had to be built on the Turtle Creek Valley branch of the Pennsylvania Rail Road. In railroad terminology the word wye would let an engineer know that there is a place to turn the locomotive.

Trafford has four borders, including Penn Township to the northeast, North Huntingdon from the east-northeast to the south, and the Allegheny County neighborhoods of North Versailles Township to the west and Monroeville to the north.