Tustin is a city in Orange County, California, United States. As of the 2006 census, the city had a total population of 70,871. The city is located next to the county seat, Santa Ana, and does not include the Tustin Foothills. The city is home to mostly middle and upper middle class residents, but some lower income persons live in Tustin as well. Unincorporated Northern Tustin contains areas of exceptional wealth, including Lemon Heights and Cowan Heights. The East side and Tustin Ranch communities are home to upper income residents.