Hatfield is a town and civil parish in Hertfordshire, England, in the borough of Welwyn Hatfield. It had a population of 29,616 in 2001, 39,201 at the 2011 Census, and 41,265 at the 2021 Census. The settlement is of Saxon origin. Hatfield House, home of the Marquess of Salisbury, forms the nucleus of the old town.