Arlington is a town in Middlesex County, Massachusetts, United States. The town is six miles (10 km) northwest of Boston, and its population was 46,308 at the 2020 census.

European colonists settled the Town of Arlington in 1635 as a village within the boundaries of Cambridge, Massachusetts, under the name Menotomy, an Algonquian word considered by some to mean "swift running water", though linguistic anthropologists dispute that translation. A larger area was incorporated on February 27, 1807 as West Cambridge, replacing Menotomy. This includes the town of Belmont, and outwards to the shore of the Mystic River, which had previously been part of Charlestown. The town was renamed Arlington on April 30, 1867 in honor of those buried in Arlington National Cemetery.

The Massachusett tribe lived around the Mystic Lakes, the Mystic River, and Alewife Brook. Chief Nanepashemet was killed by a rival tribe in about 1619, and Nanepashemet's widow "Squaw Sachem of Mistick" became the acknowledged leader of the tribe. In 1639, she deeded the land of what was then Cambridge and Watertown to the colonists. She lived her last years on the west side of the Mystic Lakes near Medford, where she died sometime between 1650 and 1667.

A stream called Mill Brook flows through the town, which historically figured largely into Arlington's economy. In 1637, Captain George Cooke built the first mill in this area. Subsequently, seven mills were built along the stream, including the Old Schwamb Mill, which still survives. The Schwamb Mill has been a working mill since 1650, making it the longest working mill in the country.

Paul Revere's midnight ride to alert colonists took him through Menotomy, now known as Arlington. Later on that first day of the American Revolution, more blood was shed in Menotomy than in the battles of Lexington and Concord combined. Minutemen from surrounding towns converged on Menotomy to ambush the British on their retreat from Concord and Lexington. Twenty-five Americans were killed in Menotomy, half of all Americans killed in the day's battles, as well as 40 British troops (more than half their fatalities). Arlington resident Cyrus Dallin would later create an iconic sculpture of the rider; a version can be seen at the town's Cyrus Dallin Art Museum.

The Jason Russell House is a museum which remembers those 12 Americans who were killed in and around this pictured dwelling on April 19, 1775. Bullet holes are visible in the interior walls to this day.

In its early years, Arlington was a thriving farming community and had its own lettuce that was quite popular. Arlington had a large ice industry on Spy Pond from the mid-19th century until the last ice house burned down in 1930; much of its ice was sent to the Caribbean and India by "Ice King" Frederic Tudor.

Arlington's population grew by over 90 percent during the 1920s. In 1979, the first spreadsheet software program VisiCalc was developed by Bob Frankston and Dan Bricklin in the attic of the Arlington apartment rented by Bob Frankston.

Arlington covers 3,517.5 acres (14 km2), or 5.5 square miles, of which 286.2 acres (1.2 km2), or 0.4 square miles, are covered by water. There are 210.52 acres (0.9 km2) of parkland. Elevation ranges from 4 feet (1.2 m) above sea level (along Alewife Brook) to 377 feet (114.9 m) near Park Avenue and Eastern Avenue.

Arlington borders on the Mystic Lakes, Mystic River, and Alewife Brook. Within its borders are Spy Pond, the Arlington Reservoir, Mill Brook, and Hills Pond.

Arlington is located in eastern Massachusetts and is bordered by the cities of Medford to the northeast, Somerville to the east, Cambridge to the southeast, and the towns of Winchester to the north, Lexington to the west, and Belmont to the south.

Several MBTA bus routes pass through the town.

The Minuteman Bikeway also runs through the center of town, connecting residents by bike to Bedford, Lexington, the Alewife Red Line station and Boston.

Route 2 is a limited access highway that runs along the southern border of Arlington with Belmont.

Historically, Arlington is known for being an Irish, Italian and Greek middle class community but in the last decades has become increasingly expensive. [citation needed] But still retaining its middle class homes with a mixture of double/triple decker homes (multiple family styles homes) and (mostly smaller sized for single family homes) single family homes.

The annual Greek festival is held in Arlington annually.

Arlington or “A-Town” (as it is referred to by Bostonians) has long a strong reputation of being a “Irish, Italian” community among Bostonians. [citation needed]

At the 2020 census, there were 46,308 people living in 19,308 households in the town. The population density was 9,004.1 people per square mile. There were 19,974 housing units at an average density of 3,841.2 per square mile (1,483.1/km2) as of the 2010 census. The racial makeup of the town as of the 2020 census was 75.6% White, 3.3% African American, 0.1% Native American, 13.7% Asian and 6.1% from two or more races. Hispanic or Latino of any race were 5.0% of the population.

There were 19,308 households with an average household size of 2.37 According to previous data, 27.0% had children under the age of 18 living with them, 45.1% were married couples living together, 2.0% had a male householder with no wife present, 9.9% had a female householder with no husband present, and 43.0% were non-families. 35.1% of all households were made up of individuals, and 11.2% had someone living alone who was 65 years of age or older.

Of the 46,308 people in the population, 6.5% were under the age of 5, 21.4% were under the age of 18, and 16% were 65 years and over. 53.3% of the population was female.

The median household income was $125,701, up from $85,059 in 2010. The per capita income for the town was $69,007, up from $47,571 in 2010. About 4.6% of the population were below the poverty line.

Data is from the 2009–2013 American Community Survey 5-Year Estimates.

Arlington's executive branch consists of an elected five-member Select Board. The day-to-day operations are handled by a Town Manager hired by the Select Board. The legislative branch is a Representative Town Meeting, presided over by the Town Moderator, and is made up of 252 Town Meeting Members. Twelve Town Meeting Members are elected to staggered three year terms from each of the 21 precincts. Article LXXXIX Section 8 of the Massachusetts Constitution permits towns with a population greater than 12,000 to adopt a city form of government. The Town of Arlington meets the population requirement to become a city, but has not done so, in part because it would lose its ability to engage citizens in local government under the Representative Town Meeting form of government. Annual Town Meetings begin in April on the first Monday after Patriots' Day, and are held two nights a week until all items on the town warrant are resolved, and generally last three to four weeks.

In April 2021, Arlington voted to become the third municipality in the United States to recognize polyamorous domestic partnerships, following adjacent cities of Somerville and Cambridge.

Arlington has a public school system with ten schools. (seven elementary schools, two middle schools and one high school) The seven elementary schools (K–5) are Brackett, Bishop, Dallin, Hardy, Peirce, Stratton, and Thompson. There are also two middle schools, grade 6 at Gibbs, and grades 7–8 at Ottoson, and Arlington High School, which includes grades 9–12. In addition, Arlington is in the district served by the Minuteman Regional High School, located in Lexington, one of the top vocational-technical schools in Massachusetts.

There are two Parochial schools, Arlington Catholic High School, and an elementary/middle school, St. Agnes School, both affiliated with St. Agnes Parish. In addition, there are two secular elementary schools, Lesley Ellis and the Alivia Elementary School.

The Greater Boston Japanese Language School (ボストン補習授業校, Bosuton Hoshū Jugyō Kō), a supplementary school for Japanese people, has its weekday office in Arlington, while it holds classes at Medford High School in Medford.