Portsmouth is a city in Rockingham County, New Hampshire, United States. At the 2020 census it had a population of 21,956. A historic seaport and popular summer tourist destination on the Piscataqua River bordering the state of Maine, Portsmouth was formerly the home of the Strategic Air Command's Pease Air Force Base, since converted to Portsmouth International Airport at Pease.

Rockingham County is a county in the U.S. state of New Hampshire. As of the 2020 census, the population was 314,176, making it New Hampshire's second-most populous county. The county seat is Brentwood. Rockingham County is part of the Boston-Cambridge-Newton, MA-NH Metropolitan Statistical Area and the greater Boston-Worcester-Providence, MA-RI-NH-CT Combined Statistical Area. Per the 2020 census, it was New Hampshire's fastest growing county from 2010 to 2020.