Strafford County is a county located in the U.S. state of New Hampshire. As of the 2010 census, the population was 123,143. Its county seat is Dover. Strafford County was one of the five original counties identified for New Hampshire in 1769. It was named after William Wentworth, 2nd Earl of Strafford in the mistaken belief that he was the ancestor of governor John Wentworth.