Carroll County is a county located in the state of New Hampshire, in the United States. As of the 2020 census, the population was 50,107,[1] making it the third-least populous county in New Hampshire. The county seat is Ossipee.[2] The county was founded in 1840 and named in honor of Charles Carroll of Carrollton,[3] who had died in 1832, the last surviving signer of the United States Declaration of Independence.