Sullivan County is a county in the U.S. state of New Hampshire. As of the 2020 census, the population was 43,063, making it the second-least populous county in New Hampshire. Its county seat is Newport.

Newport is a town in and the county seat of Sullivan County, New Hampshire, United States. It is 43 miles (69 km) west-northwest of Concord, the state capital. The population of Newport was 6,299 at the 2020 census. A covered bridge is in the northwest. The area is noted for maple sugar and apple orchards. Prior to county division in 1827, Newport was in Cheshire County. The central part of town, where 4,735 people resided at the 2020 census, is defined as the Newport census-designated place (CDP) and is located next to the Sugar River at the junction of New Hampshire routes 10 and 11. The town also includes the villages of Kelleyville, Guild, and North Newport.