Mifflin is a borough in Juniata County, Pennsylvania, United States. The population was 642 at the 2010 census.
Mifflin was founded as the town of Patterson. At one time, Mifflin, as well as the small community of Denholm lying directly north of the town, was an important stop along the Pennsylvania Railroad. The railroad tracks still pass through the town, but they are now owned by the Norfolk Southern Railway.