Newcastle, CA has a population of 1,249 and is the 13,785th largest city in the United States. The population density is 522 per sq mi which is 125% higher than the California average and 476% higher than the national average. The median age in Newcastle is 51 which is approximately 41% higher than the California average of 36. In Newcastle, 55% of the population over 15 years of age are married, 87% speak English and 4% speak Spanish. 69% of Newcastle residents were born in California, 21% were born out of state, 4% were born outside of the United States and 6% were foreign born.