Janesville, CA has a population of 1,283 and is the 13,627th largest city in the United States. The population density is 97 per sq mi which is 58% lower than the California average and 7% higher than the national average. The median age in Janesville is 47 which is approximately 30% higher than the California average of 36. In Janesville, 76% of the population over 15 years of age are married, 98% speak English and 1% speak Spanish. 59% of Janesville residents were born in California, 38% were born out of state, 0% were born outside of the United States and 3% were foreign born.