Carroll County is a county located in the state of New Hampshire, in the United States. As of the 2010 census, the population was 47,818, making it the third-least populous county in New Hampshire. The county seat is Ossipee. The county was founded in 1840 and named in honor of Charles Carroll of Carrollton, who had died in 1832, the last surviving signer of the United States Declaration of Independence.