Adjacent counties

• Belknap County (northeast)
• Strafford County (east)
• Rockingham County (southeast)
• Hillsborough County (south)
• Sullivan County (west)
• Grafton County (northwest)

National protected area

• John Hay National Wildlife Refuge

2000 census

As of the census^[13] of 2000, there were 136,225 people, 51,843 households, and 35,460 families living in the county. The population density was 146 inhabitants per square mile (56/km²). There were 56,244 housing units at an average density of 60 units per square mile (23/km²). 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. 1.00% of the population were Hispanic or Latino of any race. 16.5% were of English, 13.4% Irish, 12.7% French, 11.0% French Canadian, 8.4% American, 6.4% German and 6.0% Italian ancestry. 94.2% spoke English, 2.9% French and 1.1% Spanish as their first language.

There were 51,843 households, out of which 33.90% had children under the age of 18 living with them, 54.90% were married couples living together, 9.80% had a female householder with no husband present, and 31.60% were non-families. 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. The average household size was 2.51 and the average family size was 3.00.

In the county, the population was spread out, with 24.90% under the age of 18, 8.10% from 18 to 24, 30.60% from 25 to 44, 24.00% from 45 to 64, and 12.40% who were 65 years of age or older. The median age was 38 years. For every 100 females, there were 97.00 males. For every 100 females age 18 and over, there were 93.70 males.

The median income for a household in the county was $48,522, and the median income for a family was $56,842. Males had a median income of $37,722 versus $27,207 for females. The per capita income for the county was $23,208. About 4.10% of families and 5.90% of the population were below the poverty line, including 6.60% of those under age 18 and 5.70% of those age 65 or over.

2010 census

As of the census of 2010, there were 146,445 people, 57,069 households, and 38,104 families living in the county.^[14] The population density was 156.8 inhabitants per square mile (60.5/km²). There were 63,541 housing units at an average density of 68.0 per square mile (26.3/km²).^[15] The racial makeup of the county was 95.3% white, 1.6% Asian, 1.0% black or African American, 0.3% American Indian, 0.3% from other races, and 1.4% from two or more races. Those of Hispanic or Latino origin made up 1.6% of the population.^[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.^[16]

Of the 57,069 households, 31.3% had children under the age of 18 living with them, 52.4% were married couples living together, 9.9% had a female householder with no husband present, 33.2% were non-families, and 25.4% of all households were made up of individuals. The average household size was 2.46 and the average family size was 2.94. The median age was 41.4 years.^[14]

The median income for a household in the county was $63,012 and the median income for a family was $75,268. Males had a median income of $50,880 versus $37,351 for females. The per capita income for the county was $30,544. About 5.2% of families and 8.1% of the population were below the poverty line, including 10.6% of those under age 18 and 7.4% of those age 65 or over.^[17]

County Commission

The executive power of Merrimack 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.^[19]

^[20]

Legislative branch

The legislative branch of Merrimack County is made up of all of the members of the New Hampshire House of Representatives from the county. In total, as of 2022^[update] there are 45 members from 30 different districts.

Cities

• Concord (county seat)
• Franklin

Towns

Census-designated places

Villages

• East Andover
• Elkins
• North Sutton
• Penacook
• South Newbury
• South Sutton