Western Massachusetts is a loosely defined geographical region of the U.S. state of Massachusetts which contains the Berkshires and the Pioneer Valley. Most commonly, the region is considered to include Berkshire, Franklin, Hampshire, and Hampden counties, though the eastern parts of the Quabbin Reservoir watershed are sometimes included.
Western Massachusetts can be divided into approximately four zones running from north to south across the region. There are 103 towns and 11 cities in Western Massachusetts, the largest of these cities being Springfield. There are also four counties in Western Massachusetts: Hampden, Franklin, Hampshire, and Berkshire.
The Pocumtuck or Nipmuck place name Achastapac (also Achatispac, Achastipak, Achatsipoag) is sometimes used interchangeably with Western Massachusetts, though this could confusingly refer to most of western New England since the Algonquian root wadchu+ash+aetai+sip+ag means "Land of mountains on both sides of a river".
The Connecticut River valley in Massachusetts is commonly known as the Pioneer Valley, having to do with a marketing campaign in the 1920s. Significant towns and cities include Greenfield, Northampton, Amherst, Easthampton, Holyoke, Chicopee, West Springfield, Springfield, East Longmeadow, Longmeadow, Ludlow, Agawam, and Westfield.
The Valley is actually an ancient downfaulted graben or rift valley that formed during the Mesozoic Era when rifting developed in the Pangaea supercontinent to separate North America from Europe and South America from Africa. Secondary rifts branched off the main crustal fracture and this one was eventually occupied by the Connecticut River. Traprock ridges—including Mount Holyoke, Mount Tom, Sleeping Giant and others, extending nearly to Long Island Sound—remain where lava penetrated the rift zone.
As continental glaciers receded near the end of the last glacial period, a moraine at Rocky Hill, Connecticut dammed the river to create ephemeral Lake Hitchcock, extending north some 200 miles (320 km.). Accumulation of fine sediments in this lake accounts for the valley's rich agricultural lands, which attracted settlers—mostly English Puritans—as early as 1636. Although many fields have been covered by urban and suburban development, the valley remains New England's most productive farmland where tobacco, tomatoes, sweet corn and other vegetables are still produced in commercial quantities.
The Hill Towns include the areas of Franklin, Hampshire, and Hampden Counties west of and above the escarpment bordering the ancient rift valley through which the Connecticut River flows. Elevations abruptly increase from about 200 feet (60 meters) to at least 1,000 feet in the escarpment zone. On top, elevations rise gradually to the west.
Most of this region is a rolling upland of schist, gneiss and other resistant metamorphics with intrusions of pegmatite and granite. Scraping by continental glaciers during the Pleistocene left thin, rocky soil that supported hardscrabble subsistence farming before the Industrial Revolution. There was hardly a land rush into such marginal land, but the uplands were slowly settled by farmers throughout most of the 1700s and organized into townships. However by 1800 better land opened up in Western New York and the Northwest Territories, so the hilltown agricultural population went into a long decline and fields reverted to forest.
The 1,000 foot (300 meter) elevation difference between uplands and the Connecticut River Valley has produced streams and rivers with gradients around 40'/mile (8 meters/km.) flowing through steep-sided valleys, notably the Westfield and Deerfield Rivers and their larger tributaries. Mills were built to exploit the kinetic energy of falling water and mill towns grew up around them, or company towns integrated production, residential and commercial activities.
The development of steam engines to free industrialization from reliance on water power brought about the so-called Second Industrial Revolution when railroads were built along the rivers to take advantage of relatively gentle grades over the Appalachians. And so as hilltop farming towns declined in importance, industrial towns in the river valleys rose to local prominence.
By convention The Berkshires are confined to Berkshire County at the western end of Massachusetts. Geologically they are a westward continuation of the hilltown uplands, and a southern extension of Vermont's Green Mountains. Maximum upland elevations increase nearly 1,000' (300 meters) from east to west, and 400' (120 meters) from south to north, so maximum elevations of The Berkshires proper are about 2,000' (600 meters) in the southwest and 2,400' (730 meters) in the northwest.
The Hilltown-Berkshire upland ends at the valley of the Housatonic River which flows south to Long Island Sound, and in the extreme north at the Hoosic River, a tributary of the Hudson. From these valleys, uplands to the east appear as a rounded mountain range, rising some 1,600 feet (500 meters). To the west, the Taconic Range rises to about 2,600' (800 meters) along the New York border. Upper tributaries of the Hoosic separate Massachusetts' highest peak, Mount Greylock 3,491' (1,064 meters) from both ranges, however its geology connects it with the Taconics. The practical limit of agriculture is somewhat below 2,000' (600 meters). Above this level climate and ecology become increasingly boreal with acidic soils. The Berkshires are known for their incredible beauty and autumn foliage.
The higher altitude area to the east of the Connecticut River valley does not have one single, common name. This area could be considered to run from Northfield, Warwick and Athol at the New Hampshire border, south to Hampden, Monson, Wales and Holland on the Connecticut border, and includes the Quabbin Reservoir. The Quabbin Region is known as the towns of Belchertown, Pelham, Ware, Hardwick, Barre, Athol, Orange, Wendell, Leverett, Shutesbury, Amherst, Phillipston, Warwick, and New Salem. The Quabbin Region, and north of it, is also locally known as the Hill Towns; a term interchangeable with the Hill Towns west of the Pioneer Valley.
The lower half of this area is known as the Quabog Hills Region, and includes towns such as Palmer and Ware. Geology is similar to the Hilltown-Berkshire uplands with resistant metamorphic rocks overlain by thin and rocky soil. With less relief, the river valleys are less pronounced, but still moderately high gradient.
Berkshire, Franklin, Hampshire and Hampden counties, in the year 2000 collectively had 814,967 residents, a population greater than that of any one of the six smallest U.S. states. The population amounted to approximately 12.84% of the 2000 population of the entire state of Massachusetts, which was 6,349,097.  Its average population density is 113.16/km² (293.07/sq mi), compared to 422.34/km² (1,093.87/sq mi) for the rest of Massachusetts, and 312.68/km² (809.83/sq mi) for the state as a whole.
This population is concentrated in cities and suburbs along the Connecticut River in an urban axis that is contiguous with greater Hartford, Connecticut. A secondary population concentration exists in the Housatonic-Hoosic valley due to the industrial heritage of Pittsfield and North Adams, and the development of tourism throughout the valley. This far-western zone is linked to New York City and Albany, New York more than with the rest of Massachusetts, however both populated zones are ultimately part of the northeast megalopolis. The rest of Western Massachusetts is lightly populated, particularly the Hilltowns where densities below 50 persons per square mile (20 per sq. km) are the rule.
In descending order of size, its largest communities are: Springfield, Chicopee, Pittsfield, Westfield, Holyoke, Northampton, Agawam, West Springfield (CDP), Amherst Center (CDP), Easthampton, Longmeadow (CDP), North Adams, and Greenfield (CDP).
Western Massachusetts was originally settled by several Native American societies including the Pocomtuc, Nonotuck Mohawk, and Mahican. The first European settlers were English Puritans who came up from Connecticut to Springfield in 1636, and from Springfield to Northampton in 1654. In 1704 the French and their Native American allies led an attack on Deerfield, Massachusetts. These early agricultural settlements were confined to the Connecticut River Valley which had New England's most productive land due to deposits of fine sediments in ancient Lake Hitchcock.
The Hill Towns west of the valley had been nearly scraped clean of soil by glaciers and were less attractive for agricultural uses. They were not settled until the early 1700s after immigration from the British Isles had shifted from Puritans to Scots-Irish. Subsistence farming predominated in this area.
After the American Revolution, a rebellion led by Daniel Shays, a farmer from East Pelham, culminated in a small battle at the federal arsenal in Springfield. Shays and his followers, the Regulators, hoped to win government reforms, including the issue of new currency and help for Continental soldiers who had incurred crushing debts while fighting for independence. Although crushed, this rebellion led Thomas Jefferson to declare that "a little revolution every twenty years or so is a good thing." Shays' Rebellion is often considered a watershed event in the creation of the United States Constitution.
- market farming in CRV, hilltown subsistence farmers move west - 1st Industrial Revolution - water power - involvement in Civil War - 2nd Industrial Revolution - steam power, railroads, upland mill towns, Horace Moses
- continued depopulation of hilltowns, flood control and water supply reservoirs - Industrial decline - growth of post-secondary education - environmentalism - Interstate Highways - suburban development
Many residents of Western Massachusetts take a critical attitude towards Boston, the state's capital and largest city. The widespread belief is that the Massachusetts legislature and executive branch know little of and care little about the western part of the state. Among the incidents that fuel this feeling:
Long a haven for small businesses, the region has expressed conflicted feelings towards giant retail corporations, leading to controversies about permitting zoning changes or variances that would allow companies such as Wal-Mart to build in local towns. The debate has been particularly strong in northern towns, particularly Greenfield, Massachusetts. 
The decline of manufacturing as the regional economic mainstay since World War II was counterbalanced in some towns and cities by growth in post-secondary education. This created new jobs and otherwise generated economic activity through land development and construction as well as having gentrifying effects. State and community-funded schools (University of Massachusetts and Westfield State College) were conspicuous in this growth, although the region's oldest institutions are noteworthy private colleges including Williams founded 1793, Amherst founded 1821, Mount Holyoke founded 1837 and Smith founded 1871.
A partial list: