Lewisburg is a borough in Union County, Pennsylvania, United States, 30 miles (48 km) south by east of Williamsport and 60 miles (97 km) north of Harrisburg. In the past, it was the commercial center for a fertile grain and general farming region. The population was 5,620 at the 2000 census. It is the county seat of Union County. Located in central Pennsylvania, on the West Branch Susquehanna River, Lewisburg is northwest of Sunbury. It is home to Bucknell University and Lewisburg Federal Penitentiary. Its 19th century downtown was recently placed on the National Register of Historic Places.