Lathrop, California is located in San Joaquin County. Below is a market update video for San Joaquin County. For detailed market report of your neighborhood, please contact us. Lathrop was platted when the railroad was extended to that point. A post office has been in operation at Lathrop since 1871. The city was named for the maiden name of the wife of Leland Stanford. In September 1869, four months after the railheads of the transcontinental railroad met at Promontory, Utah, the completion of the San Joaquin River Bridge at Mossdale crossing at Lathrop actually completed the west coast link.