Easthampton was first settled by European immigrants beginning in 1664 and was originally part of Northampton. In 1785, Easthampton was established as a “district” by Massachusetts (a former type of political entity with less independence than a town), and in 1809, it was incorporated as a town. Easthampton is the youngest town in Hampshire County by date of incorporation. (It was not, however, the last incorporated; two of the three disincorporated towns of the Quabbin Reservoir in Hampshire County, Enfield and Prescott, were incorporated afterwards.)

The town grew primarily around the Manhan River, both through its phase as a strictly agricultural community and later, through the Industrial Revolution, when mills and factories were first built in Easthampton, mainly in connection with textile manufacturing and its offshoots. The first of these, the Williston-Knight Button Company, was established in 1847 by Samuel Williston, son of the town’s first minister, a Congregationalist named Payson Williston. The company specialized in cloth-covered buttons – a coveted item at the time – and to facilitate the operation of the machinery, a local brook was dammed, creating Nashawannuck Pond. Other mills soon opened nearby, a number of them specializing in elastic and rubber thread manufacturing.

Following this spurt of industrial development, the town’s first high school and first national bank opened in 1864, and a town hall was built in 1869. Constables were replaced by the town’s first police officer in 1871, the same year that Easthampton became a regular stop on the railroad. The town’s public library opened in 1881, and fourteen years later in 1895 the community was introduced to two new innovations, telephones and streetcars. With the influx of new residents came a number of new churches, founded for Catholic, Episcopalian, Lutheran, and Methodist parishioners, as well as a second Congregational church. In 1899, the West Boylston Manufacturing Company and the Hampton Company, both specializing in cloth production, moved to Easthampton, recruiting a larger immigrant labor force, particularly from Poland and Canada.

During World War I, the town’s mills all obtained federal wartime contracts and did well financially, but long before the Great Depression hit, many factories owners were already laying off employees, seeking mergers with other companies, or looking for buyers for their facilities.

World War II provided some relief for the Easthampton economy, as several of the older textile companies as well as newer heavy manufacturing corporations received another round of federal contracts. However, beginning in the early 1960s a number of critical closures hit the town hard. Revitalization attempts began with the opening of a new industrial park and continued with a joint government-private industrial mall which has failed to solve significantly higher rates of unemployment and poverty compared to Hampshire County.

Small farms and well-established small businesses remain the economic core of Easthampton. Easthampton changed its charter in 1996 to become a city. The downtown area since 1996 has attracted a small community of artists and young people migrating due to Easthampton’s lower cost of living compared to nearby Northampton, a hub of the bohemian community regionally. Small stores around Main Street, Union Street, and Cottage Street have changed business due to the influx of this new demographic. This growth has produced new arts and cultural events such as the monthly Art Walk Easthampton, held each “Second Saturday”, in which visual, music and performance artists showcase their talents at venues around the city. In November 2018, the administration of Massachusetts Governor Charlie Baker announced a $3.5 million grant through the MassWorks program to the Ferry Street Mill redevelopment project in the city.

Easthampton is just south of the geographic center of Hampshire County. It is bordered by Southampton and Westhampton to its west, by Holyoke in Hampden County to its east and south, and by Northampton to its north. It also has a river boundary with Hadley to its northeast across the Connecticut River. The western flanks of Mount Tom and Mount Nonotuck form its eastern boundary.

Massachusetts Route 10 passes through the center of Easthampton as Main Street and Northampton Street, leading northeast 5 miles (8 km) to the center of Northampton and southwest 4 miles (6 km) to Southampton. Massachusetts Route 141 (Union Street, Cottage Street, and Holyoke Street) leads southeast from the center of Easthampton 6 miles (10 km) past Mount Tom to Holyoke. Interstate 91 and U.S. Route 5 cross the northeast tip of Easthampton near the Connecticut River, leading north to Northampton and south to Holyoke.

According to the U.S. Census Bureau, the city of Easthampton has a total area of 13.6 square miles (35.2 km²), of which 13.3 square miles (34.5 km²) are land and 0.3 square miles (0.7 km²), or 2.02%, are water. The Manhan River crosses Easthampton north of the city center, flowing into The Oxbow, a former channel of the Connecticut River, at the northeast end of the city.

As of the census of 2010, there were 16,053 people, 7,224 households, and 4,066 families residing in the city. The population density was 1,192.1 people per square mile (460.2/km²). There were 7,615 housing units at an average density of 527.9 per square mile (203.8/km²). The racial makeup of the city was 93.6% White, 3.7% Hispanic, 1.1% African American, 0.2% Native American, 2.4% Asian, <0.1% Pacific Islander, 1.1% from other races, and 1.6% from two or more races.

There were 7,224 households, out of which 21.6% had children under the age of 18 living with them, 42.2% were married couples living together, 10.4% had a female householder with no husband present, and 43.7% were non-families. 33.9% of all households were made up of individuals, and 25.1% had someone living alone who was 65 years of age or older. The average household size was 2.21 and the average family size was 2.85.

In the city, the population was spread out, with 18.0% under the age of 18, 7.5% from 18 to 24, 32.4% from 25 to 44, 24.8% from 45 to 64, and 14.1% who were 65 years of age or older. The median age was 43 years. For every 100 women and girls, there were 92.5 men and boys. For every 100 women age 18 and over, there were 89.7 men.

The median income for a household in the city was $45,185, and the median income for a family was $54,312. Men had a median income of $36,446 versus $28,756 for women. The per capita income for the city was $21,922. About 5.9% of families and 8.9% of the population were below the poverty line, including 15.0% of those under age 18 and 9.9% of those age 65 or over.

Easthampton was first established in 1785 as a town, with a board of selectmen acting as the executive. It had a town meeting form of legislature. Local voters enacted their newest charter in July 1996, establishing a city form of governance while retaining the name “Town” in its official name. Michael Tautznik was elected the first mayor of Easthampton in September 1996, after a charter was passed making the mayor the chief executive officer. The town council replaced town meeting as the legislative branch and consists of four at-large members and five district councilors. In 1999 the mayor and council petitioned the General Court to remove the word “town” from its name and to replace the word town with “city”.^{[citation needed]} Mayor Tautznik was elected to an eighth term in November 2010. In November 2013, Karen Cadieux was elected mayor after Mayor Tautznik did not seek reelection. In 2017, lawyer Nicole LaChapelle defeated long-time district councilor Joy Winnie to become the city’s next mayor.