North Tustin, California. North Tustin is a census-designated place and unincorporated community in Orange County, California. The population was 24,917 at the 2010 census, up from 24,044 at the 2000 census. It is Orange County's largest census-designated place. It is outside the city limits of Tustin and has a 92705 ZIP Code. The name was changed from Tustin Foothills in 2005.