Monroe is a town in Franklin County, Massachusetts, United States. The population was 118 at the 2020 census. By area, population, and population density, it is the smallest town in the county; and is the second-smallest town by population in the Commonwealth, with only Gosnold having fewer residents.

Franklin County is a nongovernmental county located in the northwestern part of the U.S. state of Massachusetts. As of the 2020 census, the population was 71,029, which makes it the least-populous county on the Massachusetts mainland, and the third-least populous county in the state. Its traditional county seat and most populous city is Greenfield. Its largest town by area is New Salem. Franklin County comprises the Greenfield Town, MA Micropolitan Statistical Area, which is included in the Springfield-Greenfield Town, MA Combined Statistical Area.