Mifflinburg is a borough in Union County, located in the Susquehanna River Valley of central Pennsylvania, United States. In 1792, Mifflinburg was settled by Elias and Catharina Youngman and 8 other families, many of them German, and the village of Mifflinsburgh was formed. It was named for Thomas Mifflin, who was governor of Pennsylvania and first governor under the PA Constitution of 1790, and a signer of The Declaration of Independence. Youngmanstown was another name based upon common nemonclature only, but not officially. In 1827, Mifflinburg, a.k.a. Youngmanstown, and another town adjacent to the east named Greenville, a.k.a. Rhodestown,, were combined and incorporated into a borough. The first horse drawn buggy and carriage manufacturing company was established in 1845; and Mifflinburg would become the Buggy and carriage manufacturing capital of the United States in the late 19th century. There are many Victorian homes and downtown business buildings. Mifflinburg is known for The Mifflinburg Buggy Museum, Buggy Day, annual authentic Christkindle Market the second weekend of December, and German Oktoberfest.