[1] Its most populous municipality is Amherst (due to seasonal student population; the largest year-round is Northampton), its largest town in terms of landmass is Belchertown, and its traditional county seat is Northampton.

[3] Hampshire County is part of the Springfield, MA Metropolitan Statistical Area.

[4] Hampshire County was constituted in 1662 from previously unorganized territory comprising the entire western part of Massachusetts Bay Colony.

It included the original towns of Springfield, Northampton, and Hadley.

By 1683, three new towns (Westfield (now Southwick), Suffield, and Enfield) had been incorporated south of Springfield.

These towns were partly or wholly in the modern state of Connecticut at the time of their incorporation.

The council itself ceased operations in 2019, due to what an appraisal of the council termed a "fundamentally flawed, unsustainable operational model"; it had no inherent source of income and lacked a regional planning function.

[7] Hampshire County is the middle section of the Pioneer Valley and the northern tip of the Hartford–Springfield Knowledge Corridor.

At the 2000 census there were 152,251 people, 55,991 households, and 33,818 families living in the county.

At the 2010 census, there were 158,080 people, 58,702 households, and 34,480 families living in the county.

[19][20][21] Hampshire County is home to what are known as the "Five Colleges", which include the University of Massachusetts flagship campus and four well-known private colleges: The Five College Consortium provides course cross-registration between the schools and funds free bus service, provided by Pioneer Valley Transit Authority, between the campuses.