Portsmouth is a city in Rockingham County, New Hampshire. It is the fourth-largest community in the county, with a population of 20,784 at the 2000 census. A historic seaport and popular summer tourist destination, Portsmouth is served by Pease International Tradeport, a former military base converted into a civilian airport and office park.
Portsmouth is drained by Sagamore Creek and the Piscataqua River. The highest point in the city is 100 feet (30 m) above sea level, within Pease International Airport.