Dover is a city in Strafford County, New Hampshire, United States. The population was 32,741 at the 2020 census, the largest in the New Hampshire Seacoast region and the 4th largest city in the state of New Hampshire. It is the county seat of Strafford County, and home to Wentworth-Douglass Hospital, the Woodman Institute Museum, and the Children's Museum of New Hampshire.