Middlefield is a town in Hampshire County, Massachusetts, United States. The population was 521 at the 2010 census. It is part of the Springfield, Massachusetts Metropolitan Statistical Area.
Middlefield was first settled in 1780 and was officially incorporated in 1783.
As of the census of 2000, there were 542 people, 213 households, and 161 families residing in the town. The population density was 22.4 people per square mile (8.7/km2). There were 263 housing units at an average density of 10.9 per square mile (4.2/km2). The racial makeup of the town was 98.89% White, 0.18% African American, 0.18% Native American, 0.18% from other races, and 0.55% from two or more races. Hispanic or Latino of any race were 0.55% of the population.
There were 213 households, out of which 28.6% had children under the age of 18 living with them, 66.7% were married couples living together, 5.2% had a female householder with no husband present, and 24.4% were non-families. Of all households 17.4% were made up of individuals, and 6.1% had someone living alone who was 65 years of age or older. The average household size was 2.54 and the average family size was 2.86.
In the town, the population was spread out, with 23.1% under the age of 18, 5.9% from 18 to 24, 31.2% from 25 to 44, 30.3% from 45 to 64, and 9.6% who were 65 years of age or older. The median age was 40 years. For every 100 females, there were 103.8 males. For every 100 females age 18 and over, there were 101.4 males.
The median income for a household in the town was $50,938, and the median income for a family was $53,889. Males had a median income of $35,208 versus $30,375 for females. The per capita income for the town was $24,137. About 7.3% of families and 8.6% of the population were below the poverty line, including 9.2% of those under age 18 and none of those age 65 or over.