Millis is a town in Norfolk County in the U.S. state of Massachusetts. It is a small town with a population of 7,891 according to the 2010 census. The town is approximately 19 miles (31 km) southwest of downtown Boston and is bordered by Norfolk, Sherborn, Holliston, Medfield, and Medway. Massachusetts state routes 109 and 115 run through Millis.
There are many areas of town-administered land, which helps to protect the environment and limit development. In addition, Millis has several wells and is home to various large farms. The Charles River runs through Millis and the town has other smaller streams and brooks; most notably Bogastowe Brook. Boggestowe Brook, named after the Indian tribe formerly inhabiting the area, rises in East Holliston and runs through Millis, emptying in Millisí South End Pond. Millis is also home to the Great Black Swamp. This swamp, covering hundreds of acres, is a very important characteristic of Millis. This swamp geographically divides Millis from its neighboring town Medway, and is a significant factor in the separation of the two towns in 1885. According to the United States Census Bureau, the town has a total area of 12.3 square miles (32 km2). Of this, 12.2 square miles (32 km2) is land and 0.1 square miles (0.26 km2) (0.90%) is water.
As of the census of 2000, there were 7,902 people, 3,004 households, and 2,162 families residing in the town. The population density was 650.0 people per square mile (250.9/km≤). There were 3,066 housing units at an average density of 252.2 per square mile (97.4/km≤).