[2] 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.

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.

[3] 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.

[4] 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.

[5] 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.