Philo is located in Anderson Valley in western Mendocino County. In the 2000 census, Philo had a population of 1,098. Situated along Indian Creek as it flows into the Navarro River, Philo is the home of KZYX , the local public radio station. Two small specialty lumber mills in Philo are all that remains of a once vigorous timber economy in Anderson Valley. Philo is the heart of the Anderson Valley wine region. (See Anderson Valley for a list of the region's winemakers.)
Two versions of how Philo was named are current: first, that its founder Cornelius Prather named it after his favorite female cousin; second, that he named it for his former home at Philo, Illinois.
Philo is located at geographical coordinates 39° 3′ 57″ North, 123° 26′ 42″ West.
In the state legislature Philo is located in the 2nd Senate District, represented by Democrat Pat Wiggins, and in the 1st Assembly District, represented by Democrat Patty Berg. Federally, Philo is located in California's 1st congressional district, which has a Cook PVI of D +10 and is represented by Democrat Mike Thompson.