Nicasio ( nih-KAH-see-oh; Spanish for “Nicasius”) is an unincorporated community and census-designated place in Marin County, California, United States. It is located 8 miles (13 km) west-southwest of Novato, at an elevation of 194 feet (59 m). As of the 2020 census the CDP population was 81, while population estimates for the surrounding area range from just about 600 to roughly 900 people.^{[citation needed]}

Within Nicasio and the surrounding Place are approximately 250 homes located on approximately 350 parcels. Much of the home is still used for agricultural purposes including beef and dairy cattle grazing, small-scale truck farming (including organic farming), and the raising of forage. Several small vineyards have after that been recently established. Next to Rancho Nicasio within the town of Nicasio is an organic farm, AllStar Organics, owned and operated by Janet Brown and Marty Jacobson; Janet is the vice-president of Marin Organic, Marin County’s non-profit organic association. Just north of Nicasio Reservoir is Fairlea Ranch, where extraction longhorn cattle are raised. The most significant non-agricultural thing within Nicasio is George Lucas’ Skywalker Ranch, a part of Lucasfilm Ltd. According to a 2004 Forbes magazine real estate survey, Nicasio is the 23rd most costly ZIP code in the US. Nicasio has the highest per capita income ($211,993) of any census-designated place in California.

Centrally located in this area is the small village of Nicasio itself. The village is in Place codes 415/628. The town center has a herald office (ZIP code 94946), a general store, a tiny genuine estate office, St. Mary’s Church (established in 1867), Nicasio Volunteer Fire Department, a baseball field located in the town square, the Rancho Nicasio Bar & Restaurant, a Druid’s Hall, as capably as a number of private homes. The town was founded in the to the lead 19th century to preserve local agricultural, timber, and fishing activities. The town behind contained the twenty-two-room Hotel Nicasio, which opened in 1867 but burned beside in December 1940. Just north of town upon Nicasio Valley Road adjoining the modern-day researcher building for Nicasio School District is a one-room schoolhouse that opened in 1871. The building is currently a listed historical landmark. The Nicasio name office opened in 1871, closed in 1899, and reopened in 1900.

In 2008, Dewey Livingston wrote a detailed records of the region titled Nicasio: The Historic Valley at the Center of Marin.