|Coordinates: 40°51′N76°43′W / 40.85°N 76.71°W|
|Founded||March 21, 1772|
|• Total||478 sq mi (1,240 km2)|
|• Land||458 sq mi (1,190 km2)|
|• Water||19 sq mi (50 km2) 4.0%%|
|• Density||204/sq mi (79/km2)|
|Time zone||UTC−5 (Eastern)|
|• Summer (DST)||UTC−4 (EDT)|
|Congressional districts||9th, 12th|
Northumberland County is a county in the Commonwealth of Pennsylvania. It is part of Northeastern Pennsylvania. As of the 2020 census, the population was 91,647.  Its county seat is Sunbury. 
The county was formed in 1772 from parts of Lancaster, Berks, Bedford, Cumberland, and Northampton Counties and named for the county of Northumberland in northern England. Northumberland County is a fifth class county according to the Pennsylvania's County Code.  Northumberland County comprises the Sunbury, Pennsylvania Micropolitan Statistical Area, which is also included in the Bloomsburg-Berwick-Sunbury, PA Combined Statistical Area. Among its notable residents, are Thomas L. Hamer a prior democratic congressman and Joseph Priestley, the Enlightenment chemist and theologian, left England in 1796 due to religious persecution and settled on the Susquehanna River. His former house, originally purchased by chemists from Pennsylvania State University after a colloquium that founded the American Chemical Society,  is a historical museum. 
Before European settlement the area was inhabited by the Akhrakouaeronon or Atrakouaehronon, a subtribe of the Susquehannock. By 1813 the area once comprising the sprawling county of Northumberland had been divided over time and allotted to other counties such that lands once occupied by Old Northumberland at its greatest extent are now found in Centre, Columbia, Luzerne, Lycoming, Mifflin, Union, Clearfield, Clinton, Montour, Bradford, Lackawanna, Susquehanna, Wyoming, Tioga, Potter, McKean, Warren, Venango, Snyder, and Schuylkill Counties.
According to the U.S. Census Bureau, the county has a total area of 478 square miles (1,240 km2), of which 458 square miles (1,190 km2) is land and 19 square miles (49 km2) (4.0%) is water. 
The county has a humid continental climate (Dfa/Dfb). Average temperatures in Sunbury range from 27.3 °F in January to 72.7 °F in July, while in Mount Carmel they range from 25.0 °F in January to 70.2 °F in July. 
The main river in Northumberland County is the Susquehanna River and the divergence of the 977 miles (1,572 km) long river into its two branches of navigable river and former divisions of the Pennsylvania Canal System. The Susquehanna River's tributaries in the county include the West Branch Susquehanna River, Chillisquaque Creek, Shamokin Creek, and the west flowing Mahanoy Creek, whose valley is a rail and road transportation corridor to Tamaqua and points thereafter either east, north, or south such that: east along rail or US 209 through Nesquehoning and historic Jim Thorpe; else northeast via Beaver Meadows leading north into Hazleton and the lower Wyoming Valley, or into the central Wyoming Valley skirting along the western Poconos via White Haven and Mountain Top; or otherwise head south through the Schuylkill Gap into Port Carbon and thence west to the Lancaster County or east via the greater Reading area into the lower Schuylkill Valley and Philadelphia. The county has mountains in the south and north, with the rest being mostly rolling hills.
|Mahanoy Mountain||433 meters|
|Big Mountain||402 meters|
|U.S. Decennial Census  |
1790–1960  1900–1990 
1990–2000  2010–2017  2010-2020 
As of the census  of 2000, there were 94,556 people, 38,835 households, and 25,592 families residing in the county. The population density was 206 people per square mile (79/km2). There were 43,164 housing units at an average density of 94 per square mile (36/km2). The racial makeup of the county was 97.09% White, 1.52% Black or African American, 0.10% Native American, 0.22% Asian, 0.02% Pacific Islander, 0.47% from other races, and 0.58% from two or more races. 1.10% of the population were Hispanic or Latino of any race. 32.5% were of German, 12.9% Polish, 9.9% American, 8.2% Italian, 8.1% Irish and 5.8% Dutch ancestry. 95.8% spoke English and 1.5% Spanish as their first language.
There were 38,835 households, out of which 27.30% had children under the age of 18 living with them, 52.40% were married couples living together, 9.60% had a female householder with no husband present, and 34.10% were non-families. 30.20% of all households were made up of individuals, and 15.50% had someone living alone who was 65 years of age or older. The average household size was 2.34 and the average family size was 2.89.
In the county, the population was spread out, with 21.90% under the age of 18, 7.00% from 18 to 24, 27.70% from 25 to 44, 24.40% from 45 to 64, and 19.00% who were 65 years of age or older. The median age was 41 years. For every 100 females there were 96.30 males. For every 100 females age 18 and over, there were 92.80 males.
|Black or African American (NH)||2,392||2.61%|
|Native American (NH)||110||0.12%|
|Pacific Islander (NH)||24||0.03%|
|Hispanic or Latino||4,151||4.52%|
The United States Office of Management and Budget  has designated Northumberland County as the Sunbury, PA Micropolitan Statistical Area (µSA). As of the 2010 census  the micropolitan area ranked 2nd most populous in the State of Pennsylvania and the 37th most populous in the United States with a population of 94,528. Northumberland County is also a part of the Bloomsburg–Berwick–Sunbury, PA Combined Statistical Area (CSA), which combines the population of Northumberland County as well as the Columbia, Montour, Snyder and Union County areas. The Combined Statistical Area ranked 8th in the State of Pennsylvania and 115th most populous in the United States with a population of 264,739.
As of November 7, 2022, there are 58,632 registered voters in Northumberland County. 
While county-level politics tend to be competitive, Northumberland is a Republican county in most statewide elections. The margins of victory in the county for the Republican presidential candidate in 2000, 2004, and 2008 have been 13, 21, and 14 percentage points, respectively. Governor Ed Rendell narrowly carried it against Lynn Swann while Republican Rick Santorum narrowly carried it against Bob Casey in 2006. The only Democratic statewide candidate to carry the county in 2008 was incumbent Auditor General Jack Wagner. In 2011, the election of Stephen Bridy resulted in a three-way split among the county commissioners.
Northumberland County Career Technology Center located in Coal Township
Central Susquehanna Intermediate Unit 16 – The primary service area consists of: Columbia, Montour, Northumberland, Snyder and Union counties in central Pennsylvania. Provides a wide variety of education related services to school districts, private and parochial schools and hame schooled students.
Under Pennsylvania law, there are four types of incorporated municipalities: cities, boroughs, townships, and, in one case, a town. The following cities, boroughs, and townships are located in Northumberland County:
Census-designated places are geographical areas designated by the U.S. Census Bureau for the purposes of compiling demographic data. They are not actual jurisdictions under Pennsylvania law. Other unincorporated communities, such as villages, may be listed here as well.
The population ranking of the following table is based on the 2010 census of Northumberland County. 
|Rank||City/Town/etc.||Municipal type||Population (2010 Census)|
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.
Snyder County is a county in the Commonwealth of Pennsylvania. As of the 2020 census, the population was 39,736. The county seat is Middleburg. Snyder County was formed in 1855 from parts of Union County.
Schuylkill County is a county in the Commonwealth of Pennsylvania. It is located in the heart of Pennsylvania's Coal Region and is part of Northeastern Pennsylvania. As of the 2020 census, the population was 143,049. The county seat is Pottsville.
Montour County is a county in the Commonwealth of Pennsylvania. It is located in Northeastern Pennsylvania. As of the 2020 census, the population was 18,136. Its county seat is Danville. The county is named for Andrew Montour, a prominent Métis interpreter who served with George Washington during the French and Indian War. It encompasses 132 sq mi, making it the smallest county by land area in the state.
Columbia County is a county in the Commonwealth of Pennsylvania. It is located in Northeastern Pennsylvania. As of the 2020 census, the population was 64,727. Its county seat is Bloomsburg. The county was created on March 22, 1813, from part of Northumberland County. It was named Columbia, alluding to the United States and Christopher Columbus.
Mount Carmel is a borough in Northumberland County, located in the Coal Heritage Region of Central Pennsylvania's Susquehanna River Valley, United States. The population was 5,725 at the 2020 census. It is located 88 miles (141 km) northwest of Philadelphia and 71 miles (114 km) northeast of Harrisburg, in the Coal Region. It is completely encircled by Mount Carmel Township.
Sunbury is a city and county seat of Northumberland County, Pennsylvania, United States. The principal city in the Sunbury, PA Micropolitan Statistical Area, it is also one of three principal cities in the Bloomsburg-Berwick-Sunbury, PA Combined Statistical Area.
Pennsylvania Route 61 is an 81.8-mile-long (131.6 km) state highway in the U.S. state of Pennsylvania. The route is signed on a north–south direction, running from U.S. Route 222 Business in Reading northwest to US 11/US 15/PA 147 in Shamokin Dam. PA 61 heads north from Reading through Berks County to Hamburg, where it meets Interstate 78 (I-78)/US 22. The route continues into the Coal Region in Schuylkill County and heads through Schuylkill Haven, Pottsville, Frackville, and Ashland. PA 61 passes through the southern part of Columbia County, where it turns west in Centralia, before it heads into Northumberland County and runs west through Mount Carmel, Kulpmont, Shamokin, and Sunbury. The route crosses the Susquehanna River into Snyder County and soon reaches its northern terminus.
Pennsylvania Route 54 is a state highway which runs for 82 miles (132 km) in eastern Pennsylvania. It runs from U.S. Route 15 (US 15), which is three miles (5 km) west of Montgomery, Lycoming County, in the west, to US 209 in Nesquehoning, Carbon County, in the east.
"Mahantongo" is a Lenape word, translated "where we had plenty of meat to eat" or "good hunting grounds." The name is shared by a creek, a valley, and a mountain in central Pennsylvania, and is a common street name in the area. The alternate spelling "Mahantango" is often found in early publications, e.g.,.
Area codes 570 and 272 are telephone area codes in the North American Numbering Plan (NANP) for the northeast quadrant of the U.S. state of Pennsylvania. The numbering plan area (NPA) includes the cities or towns of Scranton, Wilkes-Barre, Williamsport, Stroudsburg, East Stroudsburg, Pittston, Carbondale, Hazleton, Clarks Summit, Towanda, Bloomsburg, Sayre, Tunkhannock, Berwick, Milford, Montrose, Honesdale, Pocono Pines, Nanticoke, Tamaqua, Shavertown, Dallas, Mahanoy City, Sunbury, Jim Thorpe, and extends as far south as Pottsville and as far west as Lock Haven. Area code 570 was created in 1998 in an split of area code 717, one of the original North American area codes. In 2013, the numbering plan area received a second area code, 272, creating an overlay plan, which required ten-digit dialing for the area.
The Great Shamokin Path was a major Native American trail in the U.S. State of Pennsylvania that ran from the native village of Shamokin along the left bank of the West Branch Susquehanna River north and then west to the Great Island. There it left the river and continued further west to Chinklacamoose and finally Kittanning on the Allegheny River.
Pennsylvania Route 901 is a 26.4-mile-long (42.5 km) state route located in eastern Pennsylvania. The western terminus of the route is at PA 61 in the Coal Township hamlet of Ranshaw. Its eastern terminus is at PA 183 in Cressona. PA 901 runs northwest-southeast through forested mountains in the Coal Region within Northumberland and Schuylkill counties. The route runs concurrent with PA 54 between Locust Gap and Merrian in Mount Carmel Township before it leaves Northumberland County for Schuylkill County. PA 901 has an interchange with Interstate 81 (I-81) and continues southeast to Minersville. The route runs concurrent with U.S. Route 209 to Pottsville before it splits south and continues to PA 183.
Shamokin Creek is a tributary of the Susquehanna River in Northumberland County, Pennsylvania, in the United States. It is approximately 32.4 miles (52.1 km) long and flows through Mount Carmel, Mount Carmel Township, Coal Township, Shamokin, Ralpho Township, Shamokin Township, Snydertown, Upper Augusta Township, and Sunbury. The watershed of the creek has an area of 137 square miles (350 km2). It experiences significant impacts by abandoned mine drainage and many abandoned mine drainage discharges are in its watershed. Various other impairments also affect parts of the creek's watershed. Shamokin Creek is in the Appalachian Mountains section of the Ridge and Valley physiographic province. Rock formations consisting of sandstone, shale, and anthracite deposits occur in the watershed.
Pennsylvania's 10th congressional district is located in the south-central region of the state. It encompasses all of Dauphin County as well as parts of Cumberland County and York County. The district includes the cities of Harrisburg and York. Prior to 2019, the district was located in the northeastern part of the state. The Supreme Court of Pennsylvania redrew the district in 2018 after ruling the previous map unconstitutional due to gerrymandering. The court added State College to the old district's boundaries while removing some Democratic-leaning areas and redesignated it the twelfth district, and they reassigned the tenth district to an area around Harrisburg and York. The new tenth district is represented by Republican Scott Perry, who previously represented the old fourth district.
Pennsylvania Route 147 is a north–south route that runs for 58.3 miles (93.8 km) along the east shore of the Susquehanna River in central Pennsylvania, United States. The southern terminus is at an interchange with U.S. Route 22 /US 322 in Reed Township. The northern terminus is at an interchange with Interstate 80 (I-80) and I-180 in Turbot Township.
Central Susquehanna Intermediate Unit #16 (CSIU), located in the Milton Industrial Park, Milton, Pennsylvania, was created by the Pennsylvania General Assembly in 1971 as one of 29 Intermediate Units in the commonwealth. Intermediate units serve a given geographic area's educational needs and function as a step of organization above that of a public school district, but below that of the Pennsylvania Department of Education. The state's goal is for IU's to meet student and community needs in a cost-effective manner by providing services best offered on a regional basis such as special education, technical education, services to public and nonpublic schools. IN 2016-17 the CSIU16 budget is $76.7 million for programs and services and $1,073,846 General operating budget.
The 107th Pennsylvania House of Representatives District is located in the Coal Region and has been represented since 2023 by Joanne Stehr.
Pennsylvania Route 405 (PA 405) is a 35.124-mile-long (56.527 km) state highway that runs in the north-central part of the U.S. state of Pennsylvania. The southern terminus of PA 61 in Sunbury. The route heads across the Susquehanna River to Northumberland and northward along the West Branch Susquehanna River through Milton, Watsontown and Muncy until entering Hughesville, where it terminates at an intersection with U.S. Route 220 (US 220).
Fort Bosley was a fort fortified in 1777 in the Susquehanna Valley frontier to protect settlers. It was one of roughly a dozen frontier forts in the immediate Susquehanna Valley region. It was located near a grist mill built by John Bosley in 1773.
Coordinates: 40°51′N76°43′W / 40.85°N 76.71°W