Hampshire County is a historical and judicial county located in the U.S. state of Massachusetts. As of the 2020 census, the population was 162,308. Its most populous municipality is Amherst, its largest town in terms of landmass is Belchertown, and its traditional county seat is Northampton. The county is named after the county Hampshire, in England. Hampshire County is part of the Springfield, MA Metropolitan Statistical Area. Together with Hampden County, Hampshire County municipalities belong to the Pioneer Valley Planning Commission.

Amherst is a city in Hampshire County, Massachusetts, United States, in the Connecticut River valley. Amherst has a council–manager form of government, and is considered a city under Massachusetts state law. Amherst is one of several Massachusetts municipalities that have city forms of government but retain "The Town of" in their official names. At the 2020 census, the population was 39,263, making it the highest populated municipality in Hampshire County. The town is home to Amherst College, Hampshire College, and the University of Massachusetts Amherst, three of the Five Colleges.