Saint John Plantation is a plantation in Aroostook County, Maine, United States, on the banks of the Saint John River. The population was 267 at the 2010 census.
According to the United States Census Bureau, the plantation has a total area of 51.5 square miles (133.5 km2), of which 50.3 square miles (130.2 km2) is land and 1.3 square miles (3.3 km2), or 2.45%, is water.
As of the census of 2000, there were 282 people, 110 households, and 78 families residing in the plantation. The population density was 5.6 people per square mile (2.2/km²). There were 147 housing units at an average density of 2.9 per square mile (1.1/km²). The racial makeup of the plantation was 100.00% White.
There were 110 households out of which 33.6% had children under the age of 18 living with them, 62.7% were married couples living together, 6.4% had a female householder with no husband present, and 28.2% were non-families. 24.5% of all households were made up of individuals and 16.4% had someone living alone who was 65 years of age or older. The average household size was 2.56 and the average family size was 3.04.
In the plantation the population was spread out with 27.7% under the age of 18, 5.3% from 18 to 24, 24.5% from 25 to 44, 27.7% from 45 to 64, and 14.9% who were 65 years of age or older. The median age was 40 years. For every 100 females there were 91.8 males. For every 100 females age 18 and over, there were 96.2 males.
The median income for a household in the plantation was $27,250, and the median income for a family was $37,500. Males had a median income of $29,375 versus $13,750 for females. The per capita income for the plantation was $13,212. About 6.6% of families and 8.1% of the population were below the poverty line, including 3.2% of those under the age of 18 and 20.9% of those 65 or over.