Portsmouth is located at the northern end of New Hampshire's short seacoast, and is bounded on the north by the Piscataqua River and on the east by the island community of New Castle.

Its downtown area is roughly bounded on the north and south by mill ponds, and is where the town was first settled in 1630.

[2] The historic district encompasses a wealth of resources associated with the economic, political, and social history of the city.

It includes fine colonial-era and Federal-era residences associated with prominent local politicians and businessmen, commercial buildings spanning more than 200 years of history, and reminders of the city's importance as a maritime center.

To the south, Strawbery Banke, a living open-air history museum, preserves a portion of the city's old waterfront, and Prescott Park represents an urban renewal endeavour providing access to the waterfront area.