West Mifflin
- County:
- Allegheny County
- County Seat:
- No
- Area (mi²):
- 14.218
- State:
- Pennsylvania
West Mifflin is a borough located in Allegheny County, Pennsylvania. West Mifflin has a 2026 population of 18,902. West Mifflin is currently declining at a rate of -0.49% annually and its population has decreased by -3.42% since the most recent census, which recorded a population of 19,571 in 2020.