A town of about 13,000 in Marin County. A place that was once a cool hippie town (like when my dad moved here in the 70s) but is now copiously trendy (but still undeniably cool.)
In recent years, Mill Valley has become a great place to be a teenage babysitter (like myself,) because young, rich couples are reproducing at an alarming rate (just go to the Depot on a Sunday morning), the fathers are always really hott, and if you aren't too pierced or tattooed you will get many jobs, because very few teens in Mill Valley babysit. Why? Because they don't need the money.
Most teenagers in Mill Valley are quite naive and narcissistic, but some of the nicest people you will ever meet once you get to know them. Even though we are rich kids, we dress casually and your popularity usually isn't based on money, it's usually looks that matter, or personality. But don't worry, because we're all good looking and most of us have charming personalities.
Did that last sentence sound conceited? That's just the Mill Valley-ness in me.
Kid: Look, Daddy, it's a Hummer with a No Blood For Oil sticker!
Dad: He must be from Mill Valley.