[4] Merrimack County comprises the Concord, NH Micropolitan Statistical Area, which in turn constitutes a portion of the Boston–Worcester–Providence, MA–RI–NH–CT Combined Statistical Area.

In 2010, the center of population of New Hampshire was located in Merrimack County, in the town of Pembroke.

The highest point in Merrimack County is Mount Kearsarge, on the border of Warner and Wilmot, at 2,937 feet (895 m).

As of the census[13] of 2000, there were 136,225 people, 51,843 households, and 35,460 families living in the county.

The racial makeup of the county was 97.08% White, 0.54% Black or African American, 0.23% Native American, 0.86% Asian, 0.02% Pacific Islander, 0.23% from other races, and 1.04% from two or more races.

24.60% of all households were made up of individuals, and 9.00% had someone living alone who was 65 years of age or older.

As of the census of 2010, there were 146,445 people, 57,069 households, and 38,104 families living in the county.

There were 63,541 housing units at an average density of 68.0 per square mile (26.3/km2).

[14] In terms of ancestry, 20.5% were English, 20.4% were Irish, 10.1% were German, 9.7% were Italian, 9.7% were French Canadian, 5.2% were Scottish, and 4.9% were American.