Townsend is a town in Middlesex County, Massachusetts, United States. The population was 9,127 at the 2020 census.

Townsend was first settled by Europeans in 1676 in an area known by indigenous people of the area as Wistequassuck, and was officially incorporated in 1732. The town was named after Charles Townshend, English secretary of state and an opponent of the Tories. The town initially used the same spelling as its namesake, but the “h” was dropped in patriotic fervor in response to the Townshend Acts of 1767. The current spelling of Townsend became official by 1780.

According to the United States Census Bureau, the town has a total area of 33.1 square miles (85.8 km), of which 32.9 square miles (85.1 km²) is land and 0.2 square mile (0.6 km) (0.72%) is water. The headwaters of the Squannacook River rise in the town’s western hills. Townsend has the largest land area of any town in Middlesex County.

Townsend is bordered by Mason, New Hampshire and Brookline, New Hampshire to the north, Pepperell to the east, Groton and Shirley to the southeast, Lunenburg to the south, and Ashby to the west.

Route 119 runs east-west through Townsend, and Route 13 runs north-south.

As of the census of 2010, there were 8,926 people, 3,240 households, and 2,483 families residing in the town. The population density was 279.8 inhabitants per square mile (108.0/km²). There were 3,516 housing units at an average density of 96.9 per square mile (37.4/km). The racial makeup of the town was 96.7% White, 0.6% Black or African American, 0.2% Native American, 0.8% Asian, 0.0% Pacific Islander, 0.4% from other races, and 1.3% from two or more races. Hispanic or Latino of any race were 1.8% of the population.