Mifflinburg is a borough in Union County, Pennsylvania, United States. The population was 3,594 at the 2000 census.
In 1792, Elias and Catharina Jungman (Youngman) and their two children, came from Fort Augusta (now Sunbury) Pennsylvania to the Buffalo Valley to settle on land given to them by Catharina’s father. They divided the land into 60’ by 120’ plots that were sold to other adventurous settlers, many of them German, and the village of Youngmanstown was formed. A few years later George Rote (Rhoade) laid out a village just east of Youngmanstown, known as Greenville or Rotestown, after George’s death. Eventually, the two settlements merged at Third Street. In 1827 the two villages combined and were incorporated. The combined village was named Mifflinburg, in honor of Thomas Mifflin, the first Governor of Pennsylvania after the 1790 Constitution.
In 1845, George Swentzel set up Mifflinburg's first buggy business. Soon other buggy manufacturers set up their own shops in Mifflinburg, and by 1855, with a population of 800, Mifflinburg hosted thirteen coachmakers. By the 1880s, with more than fifty buggy and sleigh factories, Mifflinburg became known as “Buggy Town” because its buggy makers produced more horse-drawn vehicles per capita than any other town in the state.