|• Total||7.732 sq mi (20.025 km2)|
|• Land||7.732 sq mi (20.025 km2)|
|• Water||0 sq mi (0 km2) 0%|
|Elevation||1,473 ft (449 m)|
|• Density||330/sq mi (130/km2)|
|Time zone||UTC-8 (PST)|
|• Summer (DST)||UTC-7 (PDT)|
|GNIS feature ID||1652814|
Winchester was founded in 1886 in Peasant Valley in what was then San Diego County. The town was named after the widow of Horace Winchester, Mrs. Amy Winchester.
Largely rural for most of its history, and home to agricultural businesses including the Winchester Cheese Company, Winchester experienced rapid growth during the housing construction boom in the early-to-mid 2000s. However, construction and growth slowed when the housing bubble burst in 2007, resulting in a housing market correction. The mid-to-late 2010s saw housing prices in Winchester recover and construction continue with new subdivisions, schools, and parks being built.
Winchester is located at (33.707871, -117.086861).
According to the United States Census Bureau, the CDP has a total area of 7.7 square miles (20 km2), all of it land.
It is approximately 8 miles southwest of the city of Hemet, California.
At the 2010 census Winchester had a population of 2,534. The population density was 327.7 people per square mile (126.5/km2). The racial makeup of Winchester was 1,577 (62.2%) White, 38 (1.5%) African American, 17 (0.7%) Native American, 46 (1.8%) Asian, 2 (0.1%) Pacific Islander, 728 (28.7%) from other races, and 126 (5.0%) from two or more races. Hispanic or Latino of any race were 1,233 persons (48.7%). 
The whole population lived in households, no one lived in non-institutionalized group quarters and no one was institutionalized.
There were 769 households, 326 (42.4%) had children under the age of 18 living in them, 425 (55.3%) were opposite-sex married couples living together, 94 (12.2%) had a female householder with no husband present, 53 (6.9%) had a male householder with no wife present. There were 54 (7.0%) unmarried opposite-sex partnerships, and 6 (0.8%) same-sex married couples or partnerships. 149 households (19.4%) were one person and 71 (9.2%) had someone living alone who was 65 or older. The average household size was 3.30. There were 572 families (74.4% of households); the average family size was 3.78.
The age distribution was 762 people (30.1%) under the age of 18, 218 people (8.6%) aged 18 to 24, 613 people (24.2%) aged 25 to 44, 649 people (25.6%) aged 45 to 64, and 292 people (11.5%) who were 65 or older. The median age was 34.6 years. For every 100 females, there were 102.6 males. For every 100 females age 18 and over, there were 104.4 males.
There were 850 housing units at an average density of 109.9 per square mile, of the occupied units 491 (63.8%) were owner-occupied and 278 (36.2%) were rented. The homeowner vacancy rate was 4.3%; the rental vacancy rate was 5.4%. 1,514 people (59.7% of the population) lived in owner-occupied housing units and 1,020 people (40.3%) lived in rental housing units.
At the 2000 census there were 2,155 people, 741 households, and 532 families in the CDP. The population density was 304.1 people per square mile (117.4/km2). There were 819 housing units at an average density of 115.6 per square mile (44.6/km2). The racial makeup of the CDP was 78.1% White, 2.0% African American, 1.5% Native American, 0.4% Asian, 0.3% Pacific Islander, 14.3% from other races, and 3.5% from two or more races. Hispanic or Latino of any race were 31.4%.
Of the 741 households 32.5% had children under the age of 18 living with them, 54.9% were married couples living together, 10.5% had a female householder with no husband present, and 28.2% were non-families. 22.0% of households were one person and 9.4% were one person aged 65 or older. The average household size was 2.9 and the average family size was 3.4.
The age distribution was 28.2% under the age of 18, 8.4% from 18 to 24, 26.1% from 25 to 44, 22.5% from 45 to 64, and 14.8% 65 or older. The median age was 37 years. For every 100 females, there were 99.9 males. For every 100 females age 18 and over, there were 98.0 males.
The median household income was $33,472 and the median family income was $39,167. Males had a median income of $26,354 versus $28,021 for females. The per capita income for the CDP was $15,028. About 9.7% of families and 13.8% of the population were below the poverty line, including 9.8% of those under age 18 and 11.6% of those age 65 or over.
Suburbs surrounding Winchester
- Sgt. Janek Pawel Pietrzak and his wife, Quiana Faye Jenkins-Pietrzak, 2008 murder victims.
- Adam Yahiye Gadahn, spokesman for al-Qaeda and adviser to Osama bin Laden, spent his childhood living on the family's farm in Winchester.
In the state legislature Winchester is located in the 37th Senate District, represented by Democrat Dave Min, and in the 65th Assembly District, represented by Democrat Sharon Quirk-Silva of Fullerton.
- "2010 Census U.S. Gazetteer Files – Places – California". United States Census Bureau.
- "Winchester". Geographic Names Information System. United States Geological Survey. Retrieved November 11, 2014.
- Riverside County, California, Place Names: Their Origins and Their Stories by Jane Davies Gunther
- "US Gazetteer files: 2010, 2000, and 1990". United States Census Bureau. 2011-02-12. Retrieved 2011-04-23.
- "2010 Census Interactive Population Search: CA - Winchester CDP". U.S. Census Bureau. Archived from the original on July 15, 2014. Retrieved July 12, 2014.
- "U.S. Census website". United States Census Bureau. Retrieved 2008-01-31.
- "Marines Suspected in Sergeant's Slaying". ABC News.
- From Staff Reports (23 April 2015). "Winchester: Adam Yahiye Gadahn's unlikely road to terror". PE.com. The Press-Enterprise. Retrieved 10 September 2019.
- "California's 42nd Congressional District - Representatives & District Map". Civic Impulse, LLC.