Somersworth is a city in Strafford County, New Hampshire, United States. The population was 11,855 at the 2020 census. Somersworth has the smallest area and third-lowest population of New Hampshire's 13 cities.

Strafford County is a county in the U.S. state of New Hampshire. As of the 2020 census, the population was 130,889. Its county seat is Dover. Strafford County was one of the five original counties identified for New Hampshire in 1769. It was named after William Wentworth, 2nd Earl of Strafford in the mistaken belief that he was the ancestor of governor John Wentworth – although they were distantly related, William had no descendants. The county was organized at Dover in 1771. In 1840, the size of the original county was reduced with the creation of Belknap County.