Grafton County is a county in the U.S. state of New Hampshire. As of the 2020 census, the population was 91,118. Its county seat is the town of Haverhill. In 1972, the county courthouse and other offices were moved from Woodsville, a larger village within the town of Haverhill, to North Haverhill. Grafton County is part of the Claremont-Lebanon, NH–VT Micropolitan Statistical Area. The county is the home of Dartmouth College and Plymouth State University.