Resident Population in Northumberland County, PA was 90.12000 Thous. of Persons in January of 2023, according to the United States Federal Reserve. Historically, Resident Population in Northumberland County, PA reached a record high of 101.90000 in January of 1978 and a record low of 90.12000 in January of 2023. Trading Economics provides the current actual value, an historical data chart and related indicators for Resident Population in Northumberland County, PA - last updated from the United States Federal Reserve on May of 2024.