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, almost one-third the population of the entire state. Its county seats are Manchester and Nashua, the state's two biggest cities. 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.
History
Hillsborough was one of the five original counties identified for the old Province of New Hampshire in 1769, and was named for Wills Hill, 1st 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 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.
Geography
According to the United States Census Bureau, the county has a total area of , of which is land and (1.8%) is water. The highest point in Hillsborough county is Pack Monadnock Mountain at .
Adjacent counties
- Merrimack County (north)
- Rockingham County (east)
- Essex County, Massachusetts (southeast)
- Middlesex County, Massachusetts (south)
- Worcester County, Massachusetts (southwest)
- Cheshire County (west)
- Sullivan County (northwest)
National protected area
- Wapack National Wildlife Refuge
Politics and government
thumb|2020 presidential election by voting ward in Hillsborough County
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. But 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. In 2024, the county voted for Democratic nominee Kamala Harris, the first time it voted for a Democrat who lost the presidential election since 1968.
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County Commission
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.
{| class=wikitable
|- valign=bottom
! District
! Commissioner
! Hometown
! Party
|-
| 1
| | Toni Pappas
| Manchester
| |Republican
|-
| 2
| | Michael Soucy
| Nashua
| |Republican
|-
| 3
| | Robert Rowe
| Amherst
| |Republican
|}
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.
{| class=wikitable
|- valign=bottom
! Office
! Name
|-
| County Attorney
| | John Coughlin (R)
|-
| Register of Deeds
| | Dennis Hogan (R)
|-
| County Sheriff
| | Christopher Connelly (R)
|-
| Register of Probate
| | Christopher Maidment (R)
|-
| County Treasurer
| | David Fredette (R)
|}
County Convention
The legislative branch of Hillsborough County, also known as the County Convention or County Delegation, is made up of all of the members of the New Hampshire House of Representatives from the county. As of 2022, there are 123 members from 45 districts.
{| class=wikitable
|- valign=bottom
! colspan="2" style="text-align:center;"| Affiliation
! Members
! Voting share
|-
|
| Democratic Party
| align=center | 72
| align=center | 58.5%
|-
|
| Republican Party
| align=center | 51
| align=center | 41.5%
|-
! colspan=2 | Total
! 123
! 100%
|}