By the 2010 census, the population had decreased to 17,456.
Greenfield, as the only community in the county with a population over 10,000, is the largest community by population or population density in the county.
 It is also the smallest mainland county seat in the Commonwealth, as only the island towns of Edgartown and Nantucket are smaller.

As of the census of 2000, there had been 18,168 people, 7,939 households, and 4,374 families residing in the city.
 The population density was 836.2 people per square mile (322.8/km²).
 There were 8,301 housing units at an average density of 382.1 per square mile (147.5/km²).
 The racial makeup of the city was 93.39% White, 1.34% Black or African American, 0.32% Native American, 1.10% Asian, 0.02% Pacific Islander, 1.41% from other races, and 2.43% from two or more races.
Hispanic or Latino of any race were 3.54% of the population.

There were 7,939 households, out of which 26.1% had children under the age of 18 living with them, 38.6% were married couples living together, 12.7% had a female householder with no husband present, and 44.9% were non-families.
36.9% of all households were made up of individuals, and 13.6% had someone living alone who was 65 years of age or older.
 The average household size was 2.19 and the average family size was 2.88.

In the town the population was spread out, with 21.9% under the age of 18, 8.4% from 18 to 24, 28.7% from 25 to 44, 23.5% from 45 to 64, and 17.5% who were 65 years of age or older.
 The median age was 40 years.
For every 100 females, there were 88.9 males.
 For every 100 females age 18 and over, there were 85.4 males.

The median income for a household in the town was $33,110, and the median income for a family was $46,412.
Males had a median income of $33,903 versus $26,427 for females.
The per capita income for the town was $18,830.
 About 11.4% of families and 14.0% of the population were below the poverty line, including 19.2% of those under age 18 and 11.1% of those age 65 or over.
By the 2010 census, the population had decreased to 17,456. Greenfield, as the only community in the county with a population over 10,000, is the largest community by population or population density in the county.  It is also the smallest mainland county seat in the Commonwealth, as only the island towns of Edgartown and Nantucket are smaller.
As of the census of 2000, there had been 18,168 people, 7,939 households, and 4,374 families residing in the city.  The population density was 836.2 people per square mile (322.8/km²).  There were 8,301 housing units at an average density of 382.1 per square mile (147.5/km²).  The racial makeup of the city was 93.39% White, 1.34% Black or African American, 0.32% Native American, 1.10% Asian, 0.02% Pacific Islander, 1.41% from other races, and 2.43% from two or more races. Hispanic or Latino of any race were 3.54% of the population.
There were 7,939 households, out of which 26.1% had children under the age of 18 living with them, 38.6% were married couples living together, 12.7% had a female householder with no husband present, and 44.9% were non-families. 36.9% of all households were made up of individuals, and 13.6% had someone living alone who was 65 years of age or older.  The average household size was 2.19 and the average family size was 2.88.
In the town the population was spread out, with 21.9% under the age of 18, 8.4% from 18 to 24, 28.7% from 25 to 44, 23.5% from 45 to 64, and 17.5% who were 65 years of age or older.  The median age was 40 years. For every 100 females, there were 88.9 males.  For every 100 females age 18 and over, there were 85.4 males.
The median income for a household in the town was $33,110, and the median income for a family was $46,412. Males had a median income of $33,903 versus $26,427 for females. The per capita income for the town was $18,830.  About 11.4% of families and 14.0% of the population were below the poverty line, including 19.2% of those under age 18 and 11.1% of those age 65 or over.
Greenfield, Massachusetts