The upper end of High Street, however, continues to develop as a retail center, with several big-box chain stores.Somersworth is bordered to the northeast by the Salmon Falls River, which is also the state boundary with Maine.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.Labor was also cheaper in the South, which did not have New Hampshire's inventory tax that levied commodities like coal and cotton at the plants.The Great Depression sent many regional textile firms into bankruptcy, when some local facilities were adapted for shoemaking.Some antique residences, most notably within the historic district known as "The Hill", have been restored.The municipality is today largely a bedroom community for other cities and the Portsmouth Naval Shipyard.
There were 5,199 housing units, of which 337, or 6.5%, were vacant.
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".
The racial makeup of the city was 89.4% white, 1.4% African American, 0.3% Native American, 5.3% Asian, 0.02% Pacific Islander, 0.9% some other race, and 2.6% from two or more races.
2.5% of the population were Hispanic or Latino of any race.