Lancaster is a town located along the Connecticut River in Coös County, New Hampshire, United States. The town is named after the city of Lancaster in England. As of the 2020 census, the town population was 3,218, the second largest in the county after Berlin. It is the county seat of Coos County and gateway to the Great North Woods Region of the state. Lancaster, which includes the villages of Grange and South Lancaster, is home to Weeks State Park and the Lancaster Fair. Part of the White Mountain National Forest is in the eastern portion. The town is part of the Berlin, NH−VT Micropolitan Statistical Area.

Coös County or Coos County is a county in the U.S. state of New Hampshire. As of the 2020 census, the population was 31,268, making it the least-populated county in the state. The county seat is Lancaster.