West Mifflin is a borough in Allegheny County, Pennsylvania, United States, located southeast of downtown Pittsburgh.

Other employers include advanced naval nuclear propulsion technology research and development facility, Bettis Atomic Power Laboratory; monorail manufacturer Bombardier; US Steel's Mon Valley Works–Irvin Plant; Community College of Allegheny County's South Campus; and the Allegheny County Airport.

The landscape is largely hilly and wooded, and the borough's eastern boundary is contiguous with the Monongahela River three separate times.

Much of the original landscape has been altered as a result of the historic dumping of steel mill byproducts such as slag and fly ash.

West Mifflin has ten land borders, including the Pittsburgh neighborhoods of Lincoln Place and Hays as well as Munhall and Whitaker, to the north, Duquesne to the east, Dravosburg to the southeast, Jefferson Hills and Pleasant Hills to the south, Baldwin to the west and also a short border with Clairton to the south.

[12] Coal mining in the area has affected the flow and water quality of small streams.

[22] The West Mifflin School District charges tuition for nearby Duquesne students to attend.

[23] Community College of Allegheny County also has its South Campus in the borough, at 1750 Clairton Road.

West Mifflin is accessible primarily by road, though no Interstate highways pass through the area.