Merrimack County is located in the central part of the state. The county seat is in Concord, which is also the state capitol.
The population in 2000 was 136,225. The largest towns are Concord, Hooksett, and Franklin.
Merrimack is bordered by Belknap County to the north, Rockingham County to the east, Hillsborough County to the south, and Sullivan County to the west.