is a city in Marin County, California, United States located about north of San Francisco via the Golden Gate Bridge. It began as a Mexican land grant to an Irish settler, John Thomas Reed, who became a Mexican citizen in 1834. He built the first saw mill in California, the "Old Mill" in Mill Valley. The population was 13,600 at the 2000 census.
Mill Valley has a mild Mediterranean climate. Daytime highs range from about 52 to in the winter, and about 60 to 74 degrees (sometimes reaching up to low 80's°) during the rest of the year. Nighttime temperatures in winter rarely drop below 38 degrees. There is abundant rainfall (sometimes per month) in the winter, and some rain in early spring and late fall. Summer temperatures vary much more than those of the winter. Much of the time, there is abundant sunshine with temperatures between 75 and 90 degrees, and humidity between 20 and 40 percent. Fog from the coast can bring cool summer weather, with midday temperatures often not exceeding 65 degrees. Since some parts of Mill Valley lack significant sunshine owing to the dense shade of redwood trees, this moist weather has earned the city the sobriquet "Mildew Valley." Nighttime summer temperatures seldom drop below 60 degrees. Summer evenings can be breezy, with warm east winds, and it is not uncommon for there to be no rainfall between mid-June and mid-October; however, dew can often be found on plants in the early morning. Because of Northern California's mild summers, few residents have air-conditioning in their homes. May through October is considered "fire season," because most water-reliant grasses die when rain ceases in May. The grasses become dry and extremely flammable, and local fire agencies prohibit most kinds of outdoor burning, fireworks, and barbecues.