Merrimack County is a county in the U.S. state of New Hampshire. Its county seat is Concord, the state capital. The county was organized in 1823 from parts of Hillsborough and Rockingham counties, and is named for the Merrimack River. Merrimack County comprises the Concord, NH Micropolitan Statistical Area, which is also included in 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.