county, central New Hampshire, U.S. It consists of a hilly upland region, bisected north-south by the Merrimack River, that becomes more mountainous in the western portion of the county. Notable peaks include Mount Kearsarge and the Summit and Ragged Mountains. Other streams include the Blackwater, Contoocook, Soucook, and Suncook rivers. Sunapee, Pleasant, and Webster lakes are among the numerous small lakes. Recreational areas include Bear Brook, Winslow, Rollins, and Mount Sunapee state parks. White pine is the dominant species of tree. The western half of the county contains several covered truss bridges.

The Hannah Duston Memorial Historic Site commemorates a clash between settlers and Abenaki Indians in Boscawen in 1697. Daniel Webster (Webster, Daniel) was born near Franklin in 1782. The village of Canterbury, founded in the late 18th century, contains a re-created Shaker community with 25 original buildings dating from as early as 1785. Colby-Sawyer College, formerly known as New London Academy, was founded in New London in 1837.

Merrimack county was formed in 1823 and named for the Merrimack River. Concord is the county seat and the New Hampshire state capital. Other communities are Hooksett, Pembroke, Hopkinton, and Allenstown. In addition to state government activities, the county is known for granite quarrying and the manufacture of electronic components and aircraft parts. Area 934 square miles (2,420 square km). Pop. (2000) 136,225; (2007 est.) 148,274.