The Merrimack County Courthouse is located at 4 Court Street, Concord NH 03301; phone: 603-228-0331. Concord, the county seat, was founded in 1823.
Merrimack County was formed in 1823 from towns of Hillsborough and Rockingham Counties. A portion of Franklin was annexed from the then Strafford County town of Sanbornton. Hill and Danbury were later added from Grafton County. Merrimack has the third largest population, but has less than half of Rockingham's and a little over one-third of Hillsborough's.