Deerfield is a town in Rockingham County, New Hampshire, United States. The population was 4,855 at the 2020 census, up from 4,280 in 2010. Deerfield is the location of the annual Deerfield Fair.

Rockingham County is a county in the U.S. state of New Hampshire. As of the 2020 census, the population was 314,176, making it New Hampshire's second-most populous county. The county seat is Brentwood. Rockingham County is part of the Boston-Cambridge-Newton, MA-NH Metropolitan Statistical Area and the greater Boston-Worcester-Providence, MA-RI-NH-CT Combined Statistical Area. Per the 2020 census, it was New Hampshire's fastest growing county from 2010 to 2020.