Union County is a county in the Commonwealth of Pennsylvania. As of the 2020 census, the population was 42,681. Its county seat is Lewisburg. The county was created on March 22, 1813, from part of Northumberland County. Its name is an allusion to the federal Union. Mifflinburg was established by legislation as the first county seat until it was moved to New Berlin in 1815. Lewisburg became county seat in 1855 and has remained so since. Union County comprises the Lewisburg, PA Micropolitan Statistical Area, which is also included in the Bloomsburg-Berwick-Sunbury, PA Combined Statistical Area. The county is part of the Central Pennsylvania region of the state.

Lewisburg is a borough in Union County, Pennsylvania, United States, 30 miles (48 km) south by southeast of Williamsport and 60 miles (97 km) north of Harrisburg. The population was 5,158 as of the 2020 census. It is the county seat of Union County. Located in central Pennsylvania's Susquehanna River Valley, on the West Branch Susquehanna River, it is home to Bucknell University. Its 19th-century downtown is listed on the National Register of Historic Places. Lewisburg is the principal city of the Lewisburg, PA Micropolitan Statistical Area, and is also part of the larger Bloomsburg-Berwick-Sunbury, PA Combined Statistical Area.