Berlin is a city along the Androscoggin River in Coös County in northern New Hampshire, United States. It is the northernmost city in New Ha…Berlin is a city along the Androscoggin River in Coös County in northern New Hampshire, United States. It is the northernmost city in New Hampshire and the only city in Coös County. The population was 9,425 at the 2020 census, down from 10,051 at the 2010 census.