Middleburg is a borough in Snyder County, Pennsylvania, United States. Located in Central Pennsylvania's Susquehanna River Valley, the borough's population was 1,325 at the 2020 census. It is the county seat of Snyder County. Middleburg is part of the Selinsgrove, PA Micropolitan Statistical Area, and is also part of the larger Bloomsburg-Berwick-Sunbury, PA Combined Statistical Area.