Carroll County is a county in the U.S. state of New Hampshire. As of the 2020 census, the population was 50,107, making it the third-least populous county in New Hampshire. Its county seat is Ossipee. The county was created in 1840 and organized at Ossipee from towns removed from Strafford County. It was named in honor of Charles Carroll of Carrollton, who had died in 1832, the last surviving signer of the United States Declaration of Independence.