Nicasio (/nɪˈkɑːsi.oʊ/ nih-KAH-see-oh; Spanish for "Nicasius") is an unincorporated community and census-designated place[7] in Marin County, California, United States.

[citation needed] Within Nicasio and the surrounding area are about 250 homes located on approximately 350 parcels.

Just north of Nicasio Reservoir is Fairlea Ranch,[9] where pedigree longhorn cattle are raised.

The most significant non-agricultural business 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 expensive ZIP code in the US.

The town center has a post office (ZIP code 94946), a general store, a tiny real estate office, St. Mary's Catholic 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 well as a number of private homes.

The town was founded in the early 19th century to support local agricultural, timber, and fishing activities.

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

It includes the south fork of Nicasio Creek extending from Moon Hill, along the ridge separating Nicasio from San Geronimo and Samuel P. Taylor State Park, and extending northwest towards the northern end of Platform Bridge Road; the east fork (Lucas Valley fork) of Nicasio Creek extending from Loma Alta and the ridge on the north side of Sir Francis Drake Boulevard, extending up through Big Rock and up towards Big Rock Ridge; the Halleck Creek drainage, up to the ridges separating Nicasio from Novato; the northern drainages extending along the ridgelines of Rocky Ridge, Hicks Mountain and Black Mountain.

Oak, bay, and fir trees are common in the area, and along some of the creeks stands of redwoods are still found.