Nicasio (ni-kash'-oh, or ni-cah'-see-oh) is a census designated place in Marin County, California. It is located 8 miles (13 km) west-southwest of Novato, at an elevation of 194 feet (59 m). A major landmark in the area is the man-made Nicasio Reservoir. Nicasio is scenically very attractive with forested and open ridgelines surrounding a wide rolling valley.
The town was founded in the early 19th century to support local agricultural, timber, and fishing activities. The town once boasted the twenty-two-room Hotel Nicasio, which opened in 1867 but burned down in December 1940. Just north of town on Nicasio Valley Road is a beautiful red-painted one-room schoolhouse that opened in 1871. The building is currently a listed historical landmark. The Nicasio post office opened in 1871, closed in 1899, and re-opened in 1900.