According to the United States Census Bureau, the CDP has a total area of 8.0 square miles (20.7 km²), all of it land.
As of the census of 2000, there were 1,160 people, 496 households, and 308 families residing in the CDP. The population density was 145.4 people per square mile (56.1/km²). There were 581 housing units at an average density of 72.8/sq mi (28.1/km²). The racial makeup of the CDP was 84.05% White, 0.09% Black or African American, 9.31% Native American, 0.26% Asian, 2.84% from other races, and 3.45% from two or more races. 9.31% of the population were Hispanic or Latino of any race.
There were 496 households out of which 27.4% had children under the age of 18 living with them, 45.0% were married couples living together, 11.5% had a female householder with no husband present, and 37.9% were non-families. 33.1% of all households were made up of individuals and 12.5% had someone living alone who was 65 years of age or older. The average household size was 2.30 and the average family size was 2.90.
In the CDP the population was spread out with 24.6% under the age of 18, 7.2% from 18 to 24, 25.0% from 25 to 44, 24.1% from 45 to 64, and 19.2% who were 65 years of age or older. The median age was 41 years. For every 100 females there were 92.1 males. For every 100 females age 18 and over, there were 91.5 males.
The median income for a household in the CDP was $23,309, and the median income for a family was $26,354. Males had a median income of $27,143 versus $24,000 for females. The per capita income for the CDP was $11,659. About 13.9% of families and 21.0% of the population were below the poverty line, including 20.2% of those under age 18 and 10.2% of those age 65 or over.
In the state legislature Greenville is located in the 1st Senate District, represented by Republican Dave Cox, and in the 3rd Assembly District, represented by Republican Dan Logue. Federally, Greenville is located in California's 4th congressional district, which has a Cook PVI of R +11 and is represented by Republican Tom McClintock.