Penngrove is a census-designated place (CDP) in Sonoma County, California, United States, situated between the cities of Petaluma and Cotati, at the foot of the western flank of Sonoma Mountain. It is part of the North Bay subregion of the San Francisco Bay Area. The population was 2,522 at the 2010 census. The area is the site of a historic grove called Penn's Grove; it was formerly a freight station on the Northwestern Pacific Railroad and a center of egg and chicken farming. Geography Penngrove's downtown consists of Main Street, a street linking Old Redwood Highway to Adobe Road. Penngrove School is located at the corner of Adobe Road, where Main Street becomes Petaluma Hill Road. Lichau Creek flows southward through the town, paralleling the railway. The creek feeds into the Petaluma River, which flows to San Pablo Bay. Due to the Sonoma Mountain's ancient volcanism, Penngrove is rich with obsidian and petrified wood. Its soil is unique, composed mainly of clay-like adobe, which has been used for centuries as building material. A prime example of adobe architecture is the Rancho Petaluma Adobe, a State Historic Park in nearby Petaluma. Penngrove enjoys a mild Mediterranean climate. According to the United States Census Bureau, the CDP covers an area of , all of it land. Demographics The 2010 United States Census reported that Penngrove had a population of 2,522. The population density was . The racial makeup of Penngrove was 2,212 (87.7%) White, 19 (0.8%) African American, 24 (1.0%) Native American, 54 (2.1%) Asian, 2 (0.1%) Pacific Islander, 112 (4.4%) from other races, and 99 (3.9%) from two or more races. Hispanic or Latino of any race were 292 persons (11.6%). The Census reported that 99.6% of the population lived in households and 0.4% lived in non-institutionalized group quarters. There were 1,040 households, out of which 260 (25.0%) had children under the age of 18 living in them, 483 (46.4%) were opposite-sex married couples living together, 117 (11.3%) had a female householder with no husband present, 65 (6.3%) had a male householder with no wife present. There were 80 (7.7%) unmarried opposite-sex partnerships, and 10 (1.0%) same-sex married couples or partnerships. 285 households (27.4%) were made up of individuals, and 83 (8.0%) had someone living alone who was 65 years of age or older. The average household size was 2.42. There were 665 families (63.9% of all households); the average family