Dover is a city in Strafford County, New Hampshire, in the United States of America. The population was 29,987 at the 2010 census, the largest in the New Hampshire Seacoast region. The population was estimated at 30,665 in 2014. 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.