Greenfield is a town in Hillsborough County, New Hampshire, United States. The population was 1,749 at the 2010 census. Greenfield is home to the Crotched Mountain Rehabilitation Center, to Greenfield State Park, and to part of the Wapack Trail. Originally known as "Lyndeborough Addition", the area was first settled by the Lynde family in 1753. Separated from the nearest church and school by the Monadnock hills, the residents successfully petitioned to form a new town in 1791, using the name "Greenfield" to highlight the area's level, fertile ground.