Thornton is a census-designated place (CDP) in San Joaquin County, California, United States. Thornton is located alongInterstate 5 7 miles (11 km) west-southwest of Galt. Thornton has a post office with ZIP code 95686. According to the United States Census Bureau, the CDP covers an area of 2.2 square miles (5.6 km²), 98.70% of it land, and 1.30% of it water.
The railroad was extended to Thornton in 1907. A post office called Thornton has been in operation since 1910. The community was named for Arthur Thornton, the original owner of the town site.