|Named for||The Earl of Hillsborough|
|Seat||Manchester and Nashua|
|Largest city||Manchester (by population) |
Weare (by area)
|• Total||892.5 sq mi (2,312 km2)|
|• Land||876.5 sq mi (2,270 km2)|
|• Water||15.9 sq mi (41 km2) 1.8%|
|• Density||470/sq mi (180/km2)|
|Time zone||UTC−5 (Eastern)|
|• Summer (DST)||UTC−4 (EDT)|
|Congressional districts||1st, 2nd|
Hillsborough County is the most populous county in the U.S. state of New Hampshire. As of the 2020 census, the population was 422,937. Its county seats are Manchester and Nashua. Hillsborough is northern New England's most populous county as well as its most densely populated.
Hillsborough County comprises the Manchester-Nashua, NH Metropolitan Statistical Area, which in turn constitutes a portion of the Boston-Worcester-Providence, MA-RI-NH-CT Combined Statistical Area.
Hillsborough County's geography is diverse, with sparsely populated rural areas in the west to suburban and urban environments in the east.
Hillsborough was one of the five original counties identified for New Hampshire in 1769, and was named for Wills Hill, the Earl of Hillsborough who was British Secretary of State for the Colonies at the time. The county was formally organized at Amherst on March 19, 1771.
In 1823, twelve townships of Hillsborough Country – Andover, Boscawen, Bradford, Dunbarton, Fishersfield (now Newbury), Henniker, Hooksett, Hopkinton, New London, Salisbury, Sutton, and Warner – became part of Merrimack County. The town of Merrimack along the Merrimack River in south-central Hillsborough County was not included in the newly-formed county 9 miles (14 km) to the north. Hillsborough County's administrative functions were moved from Amherst to Milford in 1866, and then to the current seats of Manchester and Nashua in 1869.
According to the U.S. Census Bureau, the county has a total area of 892 square miles (2,310 km2), of which 876 square miles (2,270 km2) is land and 16 square miles (41 km2) (1.8%) is water. The highest point in Hillsborough county is Pack Monadnock Mountain at 2,290 feet (700 m).
In the 2012 presidential election, Time had listed Hillsborough as one of five critical counties affecting the outcome in the swing state of New Hampshire. Obama ended up winning with a margin of 50%–49%. Despite its more urban nature, Hillsborough County has historically been a more Republican leaning part of the state, although there is evidence to suggest that is changing. In 2020, Joe Biden and Jeanne Shaheen won Hillsborough County by a wider margin than they won statewide by. Biden also received the highest percentage of the vote for a Democrat since Lyndon Johnson's 1964 landslide, largely driven due to large swings to Democrats in the county's historically Republican suburban communities.
The executive power of Hillsborough County's government is held by three county commissioners, each representing one of the three commissioner districts within the county.
In addition to the county commission, there are five directly elected officials; they include county attorney, register of deeds, county sheriff, register of probate, and county treasurer.
|County Attorney||John Coughlin (R)|
|Register of Deeds||Mary Ann Crowell (D)|
|County Sheriff||Christopher Connelly (R)|
|Register of Probate||Elizabeth Ann Moreau (R)|
|County Treasurer||David Fredette (R)|
The legislative branch of Hillsborough County is made up of all of the members of the New Hampshire House of Representatives from the county. In total, as of 2021 there are 122 members from 45 different districts.
|U.S. Decennial Census|
|White, not Hispanic or Latino||83%|
|Hispanic or Latino||8%|
|Black or African American||3%|
As of the 2020 United States census, there were 422,937 people residing in the county. The population density was 482.8 inhabitants per square mile (186.4/km2).
The racial makeup of the county was 81.0% white, 4.8% Asian, 3.9% black or African American, 1.7% American Indian, 2.1% from other races, and 2.0% from two or more races. Those of Hispanic or Latino origin made up 8% of the population.
For the period 2011–2015, 24.8% of the county's population had French ancestry (including 9.9% of the total population with French Canadian ancestry), 20.9% had Irish, 13.1% had English, 10.2% had Italian, and 8.2% had German ancestry. For the same time period, the estimated median annual income for a household in the county was $71,244, and the median income for a family was $85,966. Male full-time workers had a median income of $60,349 versus $44,270 for females. The per capita income for the county was $35,242. About 5.8% of families and 8.8% of the population were below the poverty line, including 11.7% of those under age 18 and 5.9% of those age 65 or over.