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

The county takes its name from the San Joaquin River. In the early 1800s Lieutenant Gabriel Moraga, commanding an expedition in the lower great California Central Valley, gave the name of San Joaquin (meaning Joachim) to a rivulet that springs from the Sierra Nevada and empties into Buena Vista Lake. San Joaquin County is also home to the site of the San Joaquin Valley's first permanent residence.