Folsom is a city in Sacramento County, California, United States. The population was 80,454 at the 2020 census.

The Nisenan tribe of Native Americans had long inhabited the area. The Gold Rush of 1849 brought violence, disease and overwhelming loss for the tribes.

Joseph Libbey Folsom purchased Rancho Rio de los Americanos from the heirs of San Francisco merchant William Alexander Leidesdorff, and laid out the town called Granite City, mostly occupied by gold miners seeking their fortune in the Sierra Nevada foothills. Though few amassed a great deal of wealth, the city prospered due to Joseph Folsom's lobbying to get a railway to connect the town with Sacramento. Joseph died in 1855, and Granite City was later renamed Folsom in his honor. The railway was abandoned in the 1980s but opened up as the terminus of the Gold Line of Sacramento Regional Transit District's light rail service in 2005. A few former gold-rush era towns are located within the city limits of Folsom, including Prairie City, Salmon Falls, and Mormon Island.

Folsom included a significant Chinese American community when it was first incorporated, but arsonists burned Folsom's Chinatown in March 1886, driving Chinese Americans out of town.

The establishment of Folsom Prison came in 1880, when the Livermore family made an agreement with the state to donate land for the prison in exchange for prison labor. They planned to build a hydro-electric dam from the American River for a sawmill. Though the sawmill did not work out, the Livermores soon realized that the natural force of running water could provide enough power to transmit to Sacramento, and the Folsom Powerhouse, now a National Historic Landmark, was opened. At the time it was opened, it had the longest overhead run of electricity (22 miles) in the country. The powerhouse operated until 1952.

Folsom Dam was built in 1956, providing flood control and water rights for the Sacramento Valley and created Folsom Lake. The dam is located on the southwest corner of the lake. The lake is an estimated 4.8 miles (7.7 km) from Granite Bay to the most southern point of Folsom Lake.

Folsom is home to Folsom Lake College, Folsom High School, Vista del Lago High School and a historic downtown district. Folsom is also home to the largest private employer in the Sacramento area, Intel.

The Folsom Plan Area allows the construction of 11,000 homes resulting in 25,000 additional residents enlarging the city of Folsom by one-third. The planned community development area of 3,250 acres (1,320 ha) south of Highway 50 includes additional housing, schools and parks along with office and commercial buildings.

According to the United States Census Bureau, the city has a total area of 34 square miles (88 km2), of which, 31.9 square miles (83 km2) of it is land and 2.4 square miles (6.2 km2) of it (9.69%) is water. Folsom is located in the foothills of the Sierra Nevada.

Carpenter Hill in Folsom has the highest elevation in Sacramento County.

Folsom's climate is characterized by long, hot, dry summers and cool, rainy winters.

Folsom is part of the Sacramento−Arden-Arcade−Roseville Metropolitan Statistical Area.

At the 2010 census Folsom had a population of 72,203. The population density was 2,971.2 inhabitants per square mile (1,147.2/km2). The racial makeup of Folsom was 53,627 (74.3%) White, 4,140 (5.7%) African American, 427 (0.6%) Native American, 9,000 (12.5%) Asian, 173 (0.2%) Pacific Islander, 1,818 (2.5%) from other races, and 3,018 (4.2%) from two or more races. Hispanic or Latino of any race were 8,064 persons (11.2%).

The census reported that 65,243 people (90.4% of the population) lived in households, 188 (0.3%) lived in non-institutionalized group quarters, and 6,772 (9.4%) were institutionalized.

There were 24,951 households, 9,796 (39.3%) had children under the age of 18 living in them, 14,399 (57.7%) were opposite-sex married couples living together, 2,195 (8.8%) had a female householder with no husband present, 1,006 (4.0%) had a male householder with no wife present. There were 1,150 (4.6%) unmarried opposite-sex partnerships, and 137 (0.5%) same-sex married couples or partnerships. 5,788 households (23.2%) were one person and 1,930 (7.7%) had someone living alone who was 65 or older. The average household size was 2.61. There were 17,600 families (70.5% of households); the average family size was 3.13.

The age distribution was 17,570 people (24.3%) under the age of 18, 5,344 people (7.4%) aged 18 to 24, 23,022 people (31.9%) aged 25 to 44, 19,358 people (26.8%) aged 45 to 64, and 6,909 people (9.6%) who were 65 or older. The median age was 37.6 years. For every 100 females, there were 114.1 males. For every 100 females age 18 and over, there were 117.9 males.

There were 26,109 housing units at an average density of 1,074.4 per square mile, of the occupied units 17,442 (69.9%) were owner-occupied and 7,509 (30.1%) were rented. The homeowner vacancy rate was 1.9%; the rental vacancy rate was 5.2%. 47,982 people (66.5% of the population) lived in owner-occupied housing units and 17,261 people (23.9%) lived in rental housing units.

At the 2000 census there were 51,884 people in 17,196 households, including 12,518 families, in the city. The population density was 2,386.7 inhabitants per square mile (921.5/km2). There were 17,968 housing units at an average density of 826.5 per square mile (319.1/km2). The racial makeup of the city was 77.89% Caucasian, 5.99% African American, 0.58% Native American, 7.19% Asian, 0.19% Pacific Islander, 4.71% from other races, and 3.43% from two or more races. Hispanic or Latino of any race were 9.47%.

Of the 17,196 households 39.1% had children under the age of 18 living with them, 61.7% were married couples living together, 8.0% had a female householder with no husband present, and 27.2% were non-families. 21.8% of households were one person and 7.1% were one person aged 65 or older. The average household size was 2.61 and the average family size was 3.08.

The age distribution was 24.2% under the age of 18, 6.6% from 18 to 24, 39.0% from 25 to 44, 21.4% from 45 to 64, and 8.8% 65 or older. The median age was 36 years. For every 100 females, there were 123.4 males. For every 100 females age 18 and over, there were 131.0 males.

According to a 2007 estimate, The median household income was $87,542, and the median family income was $109,032. Males had a median income of $60,616 versus $42,434 for females. The per capita income for the city was $30,210. About 2.6% of families and 7.3% of the population were below the poverty line, including 4.1% of those under age 18 and 4.3% of those age 65 or over.

According to the city's 2020 Comprehensive Annual Financial Report, the top employers in the city are:

The total Folsom labor force is 35,500. Approximately 59.6% of the total adult population asset, of around 59,740.

The city operates the Folsom Public Library, located in the Georgia Murray Building.

Livermore Community Park is located in Folsom and offers a bike trail, sports facilities and a water park. Bike trails include Humbug-Willow Creek Trail, Folsom Rail Trail, Folsom Lake Trail, and Oak Parkway Trail. Folsom is the endpoint of the American River Bike Trail, which starts in Sacramento. Bridges located in Folsom include the Lake Natoma Crossing; the Rainbow Bridge, a historic truss bridge; and Folsom Lake Crossing. There is also a pedestrian bridge over East Bidwell Street that opened on November 6, 2010, as part of a new segment on the Humbug-Willow Creek Trail called the Johnny Cash Trail and a Johnny Cash Bridge crossing over near the intersection of Folsom Lake Crossing and East Natoma that was unveiled on October 4, 2014.

In the California State Legislature, Folsom is in the 1st Senate District, represented by Republican Brian Dahle, and in the 6th Assembly District, represented by Democrat Kevin McCarty.

Located within California's 3rd congressional district, Folsom is represented in the U.S. House of Representatives by Republican Kevin Kiley.

Folsom Lake College is a public community college which is part of the Los Rios Community College District.

Folsom Cordova Unified School District operates public schools in Folsom and Rancho Cordova. The 3 high schools are Folsom High School, Vista del Lago High School, and Cordova High School. The 4 middle schools are Folsom Middle School, Sutter Middle School, Mills Middle School, and Mitchell Middle School.

The Sacramento Regional Transit District extended the light rail train system to Folsom via an extension to the Gold Line in October 2005, providing direct service to Downtown Sacramento. Regional Transit also operates the Folsom Stage Line, a public bus service within the city of Folsom.

In February 2020, 75 project customers, including the City of Folsom, received permanent federal water contracts for the Central Valley Project.