Brookline is a town in Norfolk County, Massachusetts, in the United States, and part of the Boston metropolitan area. Brookline borders six of Boston’s neighborhoods: Brighton, Allston, Fenway–Kenmore, Mission Hill, Jamaica Plain, and West Roxbury. The city of Newton lies to the west of Brookline. Brookline was first settled in 1638 as a hamlet in Boston, known as Muddy River; it was incorporated as a separate town in 1705.

At the time of the 2020 United States Census, the population of the town was 63,191. It is the most populous municipality in Massachusetts to have a town (rather than city) form of government.

Once part of Algonquian territory, Brookline was first settled by European colonists in the early 17th century. The area was an outlying part of the colonial settlement of Boston and known as the hamlet of Muddy River. In 1705, it was incorporated as the independent town of Brookline. The northern and southern borders of the town were marked by two small rivers or brooks, which is the town’s namesake. The northern border with Brighton (which was itself part of Cambridge until 1807) was Smelt Brook. (That name appears on maps starting at least as early as 1852, but sometime between 1888 and 1925 the brook was covered over.) The southern boundary, abutting Boston, was the Muddy River.

In 1843, deeds in Brookline forbade resale of property to “any negro or native of Ireland.”

The Town of Brighton was merged with Boston in 1874, and the Boston-Brookline border was redrawn to connect the new Back Bay neighborhood with Allston-Brighton. This merger created a narrow strip of land along the Charles River belonging to Boston, cutting Brookline off from the shoreline. It also put certain lands north of the Muddy River on the Boston side, including what are now Kenmore Square and Packard’s Corner. The current northern border follows Commonwealth Avenue, and on the northeast, St. Mary’s Street. When Frederick Law Olmsted designed the Emerald Necklace of parks and parkways for Boston in the 1890s, the Muddy River was integrated into the Riverway and Olmsted Park, creating parkland accessible by both Boston and Brookline residents.

Throughout its history, Brookline has resisted being annexed by Boston, in particular during the Boston–Brookline annexation debate of 1873. The neighboring towns of West Roxbury and Hyde Park connected Brookline to the rest of Norfolk County until they were annexed by Boston in 1874 and 1912, respectively, putting them in Suffolk County. Brookline is now separated from the remainder of Norfolk County.

Brookline has long been regarded as a pleasant and verdant environment. In the 1841 edition of the Theory and Practice of Landscape Gardening, Andrew Jackson Downing described the area this way: