Once a sprawling expanse, Northumberland County has been carved into twenty-one modern Pennsylvania counties.

Countries & Cities · Published 15 October 2026 Swipe more like this →

In short: Formed in 1772, Northumberland County was once a vast territory that spanned much of central and northern Pennsylvania. Over time, its original land was partitioned to create twenty-one other counties, leaving behind the smaller, distinct region that exists today as a fifth-class county centered around the Susquehanna River.

The history of Northumberland County is defined by its dramatic contraction. At its greatest extent, the county encompassed lands that now constitute twenty-one separate counties, including Centre, Columbia, Luzerne, Lycoming, and Bradford. This massive original territory was gradually subdivided, with the remaining area now covering 478 square miles. Of this total, about 4.0% is water, primarily dominated by the Susquehanna River and its tributaries, such as the West Branch Susquehanna, Chillisquaque, Shamokin, and Mahanoy Creeks.

The region's economic identity underwent a significant shift in the mid-20th century. Historically, the landscape was defined by anthracite coal mining and manufacturing, which served as the primary employers for the local population. However, beginning in the 1950s, the gradual closure of these mines and the departure of factories triggered a period of economic depression and population decline. This transition marked a departure from the industrial era that had shaped the county's development for generations.

Today, the county functions as a micropolitan statistical area with a population of 91,647 as of the 2020 census. Its seat, Sunbury, sits within a region characterized by rolling hills and mountains in the north and south. The area maintains a humid continental climate, with average January temperatures in Sunbury reaching 27.3 °F. Beyond its geography, the county is noted for its historical connections to figures like Joseph Priestley, the Enlightenment chemist who settled along the Susquehanna River in 1796 after fleeing religious and political persecution in England.

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