San Joaquin County was one of the original counties of California, created in 1850 at the time of statehood.

The county was named after the San Joaquin River, which runs through it. In the early 19th century, Lieutenant Gabriel Moraga, commanding an expedition in the lower great California Central Valley, gave the name of San Joaquin (meaning Joachim) to the San Joaquin River, which springs from the southern Sierra Nevada. San Joaquin County is the site of the San Joaquin Valley’s first permanent residence.

Prior to incorporation in 1850, the area now encompassing San Joaquin County was inhabited by the Yokuts and Miwok native peoples. These communities lived in villages throughout the region, consuming diverse diets that reflected the flora and fauna of the California Delta. Acorns from Valley Oak trees, salmon from the San Joaquin, Mokelumne, Calaveras, and Stanislaus rivers, and Tule Elk were staples of the native diet, which was supplemented with various native berries and plants. The native population of San Joaquin County fell dramatically during a statewide epidemic of malaria in 1828, and a subsequent rebellion of native peoples in the Central Valley, led by Chief Estanislao.

Between 1843 and 1846, during the era when California was a province of independent Mexico, five Mexican land grants were made in what would become San Joaquin County: Rancho Campo de los Franceses, Pescadero (Grimes), Pescadero (Pico), Sanjon de los Moquelumnes, and Thompson. The largest of these grants was the Rancho Campos de los Franceses, secured by Charles Weber and Guillermo Gulnac, which was eventually developed into the city of Stockton.

As the Gold Rush drew miners to the Sierra Nevada, Stockton grew into a major logistical and mercantile hub for the San Joaquin Valley and mother lode, which allowed for the City and County populations to rise significantly between 1850 and 1870. As the state’s gold economy waned in the 1870s, San Joaquin County transitioned into a major national center of agriculture, which it remains to this day. Reclamation of the California delta, which began in 1869, strongly benefited this agricultural growth. The importance of agriculture to the region’s economy led to the creation of a dynamic industrial engineering sector in Stockton, Lodi, and nearby Rio Vista in the 1880s. Notably, the Sperry Flour Company, Holt Manufacturing Company, the operation of R. G. LeTourneau, Samson Ironworks, and the canning empire of Tillie Lewis were firms of national and international significance. Holt Manufacturing, led by Benjamin Holt, would pioneer the industrial manufacturing and sales of the tractor, while R. G. LeTourneau patented the bulldozer in 1926.