Lathrop, CA has a population of 20,331 and is the 2,138th largest city in the United States. The population density is 927 per sq mi which is 299% higher than the California average and 923% higher than the national average. The median age in Lathrop is 33 which is approximately 9% lower than the California average of 36. In Lathrop, 57% of the population over 15 years of age are married, 49% speak English and 29% speak Spanish. 57% of Lathrop residents were born in California, 11% were born out of state, 1% were born outside of the United States and 31% were foreign born.