Coös County (/ˈkoʊ.ɒs/, with two syllables), frequently spelled Coos County, is a county in the state of New Hampshire, in the United States. As of the 2010 census, the population was 33,055, the least of any New Hampshire county. The estimated population as of 2017 is 31,634. The county seat is Lancaster.
Coös County was founded in 1803.