Nicasio is an unincorporated community and census-designated place in Marin County, California, United States. It is located 8 miles west-southwest of Novato, at an elevation of 194 feet. As of the 2020 census the CDP population was 81, while population estimates for the surrounding area range from about 600 to about 900 people. Within Nicasio and the surrounding area are about 250 homes located on approximately 350 parcels.