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.
In 1953, the Crotched Mountain Rehabilitation Center began operation in Greenfield. Established by Harry Gregg, the facility on Crotched Mountain originally treated for polio, cerebral palsy, spina bifida and other physical and neurological disabilities. A center for adult rehabilitation would open in 1961, and a rehabilitation center for adults with brain injuries in 1986. The complex today provides service to over 2,000 children and adults. In 2004, it unveiled the first wheelchair-accessible treehouse in New Hampshire.
Greenfield is home to the Yankee Siege, considered the most powerful (current) trebuchet in the world, which has participated in the annual World Championship Punkin' Chunkin' Contest in Sussex County, Delaware since 2004. The farthest official toss is as of 2008, although there are unofficial reports of throws as of 2009.