Vacaville is a city located in Solano County, California, United States. It is located 35 miles (56 km) from Sacramento and 55 miles (89 km) from San Francisco, it is on the edge of the Sacramento Valley in Northern California. The city was founded in 1851 and is named after Juan Manuel Vaca.

As of the 2020 census, Vacaville had a population of 102,386, making it the third-largest city in Solano County.

Prior to European contact, the indigenous Patwin tribe lived in the area with the Ululato tribelet establishing a chiefdom around the Ululato village in what is now downtown Vacaville along the Ulatis Creek.

The early settler pioneers of the land were Juan Manuel Cabeza Vaca and Juan Felipe Peña, who were awarded a 44,000-acre (18,000 ha) Mexican land grant in 1842. The same year, Vaca and Peña's families settled in the area of Lagoon Valley. Peña's Adobe home is the oldest standing building, built in 1842, now at Peña Adobe Park.

Discussions for the sale of a portion of land to William McDaniel began in August 1850. A written agreement was signed on December 13, 1851, forming a township, nine square miles of land were deeded to William McDaniel for $3,000, and the original city plans were laid out from that. In the agreement, McDaniel's would name the new town after Juan Manuel Cabeza Vaca.

In 1880, Leonard Buck created the California Fruit Shipping Association, and the L.W. and F.H. Buck Company, an early company auctioning fruit in the state, and Vacaville was soon home to many large produce companies and local farms, which flourished due to the Vaca Valley's rich soil. Because of Vacaville's flourishing agricultural industry, as well as an increasing number of immigrants coming into the United States, Vacaville had a large Japanese and Chinese population. While their professions varied, many of these Japanese and Chinese worked for the fruit companies in Vacaville.

It officially became a city in 1892.

In 1885, the first grade school built was Ulatis School. In 1898, the town's first high school was built, Vacaville Union High School.

In 1968, the Vacaville Heritage Council was established.

In August 2020, parts of Vacaville were evacuated due to the Hennessey Fire, which resulted in the burning of over 315,000 acres (127,476 ha) in five counties, including in Vacaville, where farms and homes were destroyed.

On August 29, 2022, a truck transporting tomatoes crashed on Interstate 80 in Vacaville, injuring four, splattering over 150,000 of the tomatoes onto the eastbound section of the freeway, and significantly delaying eastbound traffic for hours. The peculiarity of the freeway accident subsequently resulted in international news coverage.

Vacaville is surrounded by the Vaca Mountains to the south and to the west and the Sacramento Valley to the north and to the east.

A number of rare and endangered species occur in the Vacaville area. Endangered plants, which have historically occurred in the vernal pool areas in and around Vacaville include Legenre limosa, Plagiobothrys hystriculus, Downingia humilis, Contra Costa goldfields (Lasthenia conjugens), and showy Indian clover (Trifolium amoenum). To this day Trifolium amoenum can still be found in Lagoon Valley Regional Park.

According to the United States Census Bureau, the city has a total area of 28.6 square miles (74 km2), of which 0.74% is covered by water. Excluding the Putah South Canal and minor local creeks, the only significant body of water within the city is the 105-acre (0.42 km2) Lagoon Valley Lake.

The unincorporated communities of Allendale and Elmira are generally considered to be part of "greater" Vacaville.

Vacaville has a typical Mediterranean climate (Köppen Csa) with hot, dry summers and cool, wet winters. Characteristic of inland California, summers can get quite hot. Autumns are warm in the early part, but quickly cool down as the wet season approaches. Winters can be cool, and often foggy, but are mild compared to other regions. Spring is a rather pleasant season with fairly mild temperatures and not so much rain. The greater majority of precipitation falls in the autumn, winter, and spring, little to none in summer.

The wettest year was 1983 with 48.9 inches (1,240 mm) and the driest year was 2012 with 5.0 inches. The most precipitation in one month was 19.83 inches (504 mm) in January 1916. The most precipitation in 24 hours was 6.10 inches (155 mm) on February 27, 1940. Snowfall is rare in Vacaville, but light measurable amounts have occurred, including 2.2 inches (56 mm) in January 1907 and 2.0 inches (51 mm) in December 1988.

According to the 2020 United States Census, Vacaville had a population of 102,386. During the period 2015–2019, on average, 2.81 people lived in a household. The American Community Survey estimated the population identified as 50.5% non-Hispanic White, 24.8% Hispanic or Latino, 10.1% Black or African-American, 8.1% of two or more races, 7.8% Asian, 0.9% native Hawaiian or other Pacific Islander, and 0.7% American Indian or Alaska Native. The same survey estimated that 22.7% of the population was under 18 and 14% was over 65 years old.

The 2010 United States Census reported that Vacaville had a population of 92,428. The population density was 3,233.5 inhabitants per square mile (1,248.5/km2). The racial makeup of Vacaville was 66.3% White, 10.3% African American, 0.9% Native American, 6.1% Asian (3.3% Filipino, 0.7% Chinese, 0.6% Indian, 0.5% Japanese, 0.3% Vietnamese, 0.3% Korean), 0.6% Pacific Islander, 8.8% from other races, and 7.0% from two or more races. Hispanics or Latinos of any race were 22.9% of the population (17.0% of Mexican, 0.9% Puerto Rican, 0.5% Salvadoran, 0.3% Nicaraguan, 0.2% Guatemalan, and 0.2% Peruvian descent).

The census reported that 91.3% of the population lived in households and 8.6% were institutionalized.

Of the 31,092 households, 37.8% had children under 18 living in them, 52.6% were opposite-sex married couples living together, 13.1% had a female householder with no husband present, 5.4% had a male householder with no wife present, 6.1% were unmarried opposite-sex partnerships, and 0.7% were same-sex married couples or partnerships; 7,053 households (22.7%) were made up of individuals, and 2,689 (8.6%) had someone living alone who was 65 or older. The average household size was 2.71. The city had 22,101 families (71.1% of all households); the average family size was 3.19.

The age distribution was 23.3% under 18, 9.7% from 18 to 24, 28.4% from 25 to 44, 28.1% from 45 to 64, and 10.5% who were 65 or older. The median age was 37.2 years. For every 100 females, there were 112.5 males. For every 100 females 18 and over, there were 115.1 males.

The 32,814 housing units had an average density of 1,148.0 units per square mile (443.2 units/km2), of which 63.4% were owner-occupied and 36.6% were occupied by renters. The homeowner vacancy rate was 2.1%; the rental vacancy rate was 6.8%. About 59.0% of the population lived in owner-occupied housing units and 32.3% lived in rental housing units.

As of the 2000 census 88,625 people were living in the city. The population density was 1,263.6/km2 (3,273/sq mi). The 28,696 housing units had an average density of 409.1/km2 (1,060/sq mi). The racial makeup of the city was 72.11% White, 10.02% African American, 0.97% Native American, 4.18% Asian, 0.45% Pacific Islander, 6.74% from other races, and 5.53% from two or more races. About 17.9% of the population were Hispanics or |Latinos of any race.

Of the 28,105 households, 20,966 were families, 41.4% had children under 18 living with them, 57.0% were married couples living together, 12.4% had a female householder with no husband present, and 25.4% were not families. About 19.2% of all households were made up of individuals, and 6.4% had someone living alone who was 65 or older. The average household size was 2.83, and the average family size was 3.24.

The median age was 34 years, and the age distribution of the population was 27.0% under 18, 9.0% from 18 to 24, 35.4% from 25 to 44, 20.3% from 45 to 64, and 8.3% who were 65 or older. For every 100 females, there were 118.4 males. For every 100 females 18 and over, there were 124.7 males.

According to the city of Vacaville, in 2019/2020, median household income was $82,513, which was 39% above the national average and 19% higher than the state average.

In 2007, the median income for a family was $63,950. Also in 2007, males had a median income of $43,527 versus $31,748 for females and per capita income for the city was $21,557. About 6.1% of the population and 4.3% of families lived below the poverty line. Of the total population, 7.4% of those under 18 and 4.8% of those 65 and older lived below the poverty line.

Biotechnology/pharmaceutical facilities are operated by Genentech, ALZA Corporation, Kaiser Permanente, and Novartis International AG. On May 14, 2014, ICON Aircraft announced they would consolidate all company functions in a new 140,000-square-foot facility in Vacaville. Two state prisons are located in Vacaville: California State Prison, Solano and California Medical Facility. The latter houses inmates undergoing medical treatments. On June 1, 2023, Roche announced that it was looking to sell its 800-employee drug manufacturing plant in Vacaville, California, or shut down the factory by 2029.

According to the city's 2021 Comprehensive Annual Financial Report, the top employers in Vacaville (excluding government agencies) are:

Public agencies also constitute major employers; however, the city does not include them in its financial reports because they do not collect employee information through the business license renewal process. Major public employers in Vacaville include the California State Department of Corrections, Vacaville Unified School District, the State Compensation Insurance Fund, and the City of Vacaville.

Between 1992 and 1995, local artist Guillermo Wagner Granizo installed 20 outdoor ceramic-tile murals, set into three freestanding walls near City Hall, entitled, "Vacaville Centennial". The murals depict various aspects of the history of the city of Vacaville, including the early pioneers Juan Manuel Vaca, Juan Felipe Peña, and William McDaniel, the early fruit industry, the first schools, Peña Adobe Park, the Nut Tree (a 1920s roadside fruit and nut stand), various parades, the annual tree lighting ceremony, "Hamburger Hill", and the factory outlet stores, among others.

The city includes several historic buildings and places, including Peña Adobe, Will H. Buck House, Pleasants Ranch, and Vacaville Town Hall.

The Vacaville Cultural Center, located at the southeast corner of Allison Drive and Ulatis Drive, houses a regional library, the Vacaville Performing Arts Theatre, an outdoor garden, and rentable event space.

The city's libraries are operated by Solano County Library. The Vacaville Town Square Library is located within downtown, north of Main Street and east of Dobbins Road. The Vacaville Cultural Center Library is located within the Cultural Center facility at the southeast corner of Allison Drive and Ulatis Drive.

The Vacaville Art Gallery, located north of Andrews Park along East Monte Vista Avenue, provides exhibitions for local artists and community members.

The city holds an annual Vacaville Fiesta Days celebration downtown, including a parade that features the public-school marching bands, gymnasts, and an electric car showcase, among other things. Other sites for tourists include the Vacaville Premium Outlets and the Nut Tree, which is home to a train for children, a carousel, and a life-size chessboard, as well as numerous stores and dining establishments. Every Friday during the summer, the city holds the CreekWalk Concert Series in downtown Vacaville. Every December, the city holds a Festival of Trees in the ice skating rink and the Tree Lighting Ceremony, in which residents gather downtown to see a 50-foot (15 m) tree illuminate and enjoy festive music played by the Jepson Band, hot chocolate, and horse-drawn carriage rides. The Jimmy Doolittle Center at the Nut Tree Airport displays aircraft from as early as 1912 and is home to the Jimmy Doolittle Shell Lockheed Vega. Displays also include personal items of General Doolittle and items related to the Doolittle Raid of 1942.

Regional and community parks include:

Vacaville is governed by a seven-member City Council with six elected by district, and one mayor elected at large. Each serving four year terms. Current alignment is Presidential Election: District 1, 3, 5. Gubernatorial Election: Mayor and District 2, 4, 6. The mayor is John Carli (elected 2022).

Vacaville is represented by California Assembly District 11 - Lori Wilson, California State Senate District 3 - Bill Dodd, and primarily by Congressional District 4 - Mike Thompson, however, a small portion in the east and southeast portion of the city is represented by Congressional District 8 - John Garamendi.

As of September 2022, there were 58,240 registered voters in Vacaville; of these, 22,198 (38.1%) are Democrats, 17,873 (30.7%) are Republicans, and 12,959 (22.3%) stated no party preference.

Vacaville is served by two public school districts: Vacaville Unified School District and Travis Unified School District. The city is also served by a community college district, private schools and colleges.

The Vacaville Unified School District (VUSD) includes the following campuses:

The Travis Unified School District (TUSD), which serves Travis Air Force Base (TAFB) and parts of Fairfield and Vacaville, includes the following campuses:

Its campuses serving Vacaville secondary students are:

Private institutions with campuses in Vacaville are:

Vacaville is within the Solano Community College District. The Vacaville campus, located along North Village Parkway, features a 70-seat lecture hall, classrooms, science and computer laboratories, and a multipurpose room for theater arts and physical education. As part of the college's Bachelor's of Biomanufacturing degree program, the campus also contains the Biotechnology and Science Building, which houses four biotech labs, two chemistry labs, two biology labs, and a wet and dry anatomy lab. Among others, it offers an associate degree in biotechnology, which could lead to employment with local industries.

Radio station KUIC is based in Vacaville.

The Vacaville Reporter is a local daily newspaper. The Daily Republic, based in Fairfield, also provides local news coverage on Vacaville.

Interstate 80 passes through Vacaville, connecting San Francisco to the southwest and Sacramento to the northeast. Interstate 505 branches off Interstate 80, connecting Vacaville to Winters before eventually reaching Interstate 5 to the north.

The Fairfield-Vacaville Hannigan station, located east of Peabody Road in neighboring Fairfield, serves Vacaville and Fairfield. The station opened in November 2017. The station is served by Capitol Corridor trains operated by Amtrak California.

The Vacaville Transportation Center, located along Allison Drive and adjacent to Interstate 80, is the main hub for commuters via bus as well as vanpools and park-and-ride to the Sacramento area and the San Francisco Bay Area. Vacaville City Coach provides local bus service. SolanoExpress, which is operated by SolTrans, provides intercity connections to Fairfield, Benicia, Davis, Walnut Creek BART, and Sacramento.

The Nut Tree Airport is located in Vacaville and is operated by the Solano County General Services Department.

The city includes two hospitals, NorthBay VacaValley Hospital, a 50-bed facility whose campus also includes the NorthBay Cancer Center and HealthSpring Fitness Center, and the Kaiser Permanente Vacaville Medical Center, a hospital and trauma center.[citation needed]