Somersworth is a city in Strafford County, New Hampshire, United States. The population was 11,766 at the 2010 census. Somersworth has the smallest area and third-lowest population of New Hampshire's 13 cities.
Somersworth, originally called "Sligo" after Sligo in Ireland, was settled before 1700 as a part of Dover. It was organized in 1729 as the parish of "Summersworth", meaning "summer town", because during that season the ministers would preach here. It was set off and incorporated in 1754 by colonial governor Benning Wentworth, and until 1849 included Rollinsford. A clerical error at incorporation contracted the name to "Somersworth". It would be incorporated as a city in 1893, before which it was also known as "Great Falls".
Situated where the Salmon Falls River drops 100 feet (30 m) over a mile, Somersworth early became a mill town, beginning with gristmills and sawmills. In 1822, the brothers Isaac and Jacob Wendell of Boston purchased for $5,000 a gristmill with its water rights at the Great Falls.