Sonoma (/səˈnoʊmə/) is a city in Sonoma County, California, United States, located in the North Bay region of the San Francisco Bay Area. Sonoma is one of the principal cities of California's Wine Country and the center of the Sonoma Valley AVA. Sonoma's population was 10,739 as of the 2020 census, while the Sonoma urban area had a population of 31,479. Sonoma is a popular tourist destination, owing to its Californian wineries, noted events like the Sonoma International Film Festival, and its historic center.

Sonoma's origins date to 1823, when Padre José Altimira and Giovanni Toscano established Mission San Francisco Solano, under the direction of Governor Luis Antonio Argüello. Following the Mexican secularization of the missions, Californio statesman Mariano G. Vallejo founded Sonoma on the former mission's lands in 1835. Sonoma served as the base of General Vallejo's operations until the Bear Flag Revolt in 1846, when American filibusters overthrew the local Mexican government and declared the California Republic, ushering in the American Conquest of California.

When the first Spaniards arrived, the area was near the northeastern corner of the Native Americans / Aboriginal peoples (Indians) of the Coast Miwok territory, with Southern Pomo to the northwest, Wappo to the northeast, Suisun and Patwin peoples to the east.

Mission San Francisco Solano is the direct predecessor to the founding of the town of Sonoma. The mission, the only to be constructed not by the Spanish but by the later Mexican authorities seeking independence and succeeding to the Royal Spanish Viceroyalty at that time, was built as part of a larger plan Governor Luis Antonio Argüello had devised to fortify the Spanish presence north of the San Francisco Bay and thus deter Russian Empire (Russia) encroachment southward from further north in Russian America (where they'd established a presence back in the 1740s, a half-century before) into the Pacific Ocean coastal region. Franciscan padre / priest José Altimira worked with Governor Argüello to plan the mission, against the desires of José Francisco de Paula Señan, then the President-General of the Spanish missions in California, who disapproved of secular government intervention into religious matters.

A decade later, the Congress of the Union (Mexican Congress) passed the Mexican secularization act of 1833, ending Roman Catholic Church mission stewardship and control of huge tracts of associated lands in California, one goal being to diminish the church's highly influential standing in California's economy and political system. Then Governor José Figueroa appointed Mariano Guadalupe Vallejo, then the Commandant of the Presidio of San Francisco, as administrator (comisionado) to oversee the closing of Mission San Francisco Solano and its conversion into a civilian town.

Governor Figueroa had received instructions from the Mexican Congress further south in the capital city of Mexico City to establish a strong presence in the region north of the San Francisco Bay to protect the area from encroachments of foreigners. An immediate concern was the further south and eastward movement to the interior of the Russian America Company from their settlements at Fort Ross and Bodega Bay on the Northern California coastline.

Figueroa's next step in implementing his instructions was to name Lieutenant Vallejo as Military Commander of the Northern Frontier and to order the Army units of officers / soldiers, arms and materiel supplies at the Presidio of San Francisco moved to the site of the recently secularized Mission San Francisco Solano. The Sonoma Barracks were then built to house the troops. Until the building was habitable, the soldiers were housed in the buildings of the old Mission. In 1834, George C. Yount, the first European American permanent settler in the Napa Valley, north of San Francisco Bay, was employed as a carpenter by Mexican Army General Vallejo.

The Governor granted Lieutenant Vallejo the initial lands (approximately 44,000 acres (178 km²)) of Rancho Petaluma immediately west of Sonoma. Vallejo was also named Director of Colonization which meant that he could initiate land grants for other colonists (subject to the approval of the governor) and the diputación (Alta California's nominal assembly / legislature).