Rancho Nicasio was a Mexican land grant of 56,807 acres (230 km2) granted to the Coast Miwok indigenous people in 1835, located in the present-day Marin County, California, a tract of land that stretched from San Geronimo to Tomales Bay. Today, Nicasio, California is at the heart of this location.
In the mid-1830s, 80,000 acres (324 km2) was promised by General Mariano Vallejo to the San Rafael Indians, whose land had been co-opted by the Mission San Rafael. The land was granted by Mexican Governor José Figueroa to the Coast Miwok of Marin County in 1835, but the Miwok claim was rejected by the Public Land Commission in 1855. José Calistro resecured a deed to 30 acres (0.1 km2) of the original rancho at Halleck Creek in 1870, and became the chief leader of the native community of Rancho Nicasio.
In 1844, Governor Manuel Micheltorena granted the 56,621-acre (229.14 km2) Rancho Nicasio to Pablo de la Guerra and John B.R. Cooper. By 1849, there were three owners — Pablo de la Guerra, Cooper, and Jasper O’Farrell. In 1850 Pablo de la Guerra sold his 30,848 acres (124.8 km2) undivided share of the ranch to Henry Wager Halleck. In 1850, Cooper sold his 16,293 acres (65.9 km2) undivided share of the ranch to Benjamin Rush Buckelew. Besides Cooper’s share of Rancho Nicasio, Buckelew also purchased Cooper’s Rancho Punta de Quentin and John Reed’s Rancho Corte Madera del Presidio. In 1851, O’Farrell sold his 9,479 acres (38.4 km2) share to James Black, the grantee of Rancho Cañada de Jonive. In 1852 Buckelew sold 7,598 acres (30.7 km2) to William Reynolds and Daniel Frink.
With the cession of California to the United States following the Mexican-American War, the 1848 Treaty of Guadalupe Hidalgo provided that the land grants would be honored. As required by the Land Act of 1851, a claim for Rancho Nicasio was filed with the Public Land Commission in 1852, and the grant patented to Black, Buckelew, Halleck, and Reynolds and Frink in 1870.
Black later bought Halleck’s share of Rancho Nicasio. Black also bought Rancho Olompali from Camilo Ynitia, the last Olompali Indian chief, in 1852. Black's daughter, Mary, married Dr. Galen Burdell. Black's wife, Maria Agustina Sais, died in Dr. Burdell's dental chair in 1864. In 1866 Black married Maria Loreto Duarte, Ygnacio Pacheco’s widow. James Black died in 1870.
- Jane Futcher (text) and Robert Conover (photographs). 1983. Marin: The Place, the People, Profile of a California County. Holt, Rinehart and Winston ISBN 0-03-057472-2
- Hoover, Mildred Brooke, Douglas E. Kyle, and Hero Rensch. 2002. Historic spots in California, Fifth edition, Stanford University Press. ISBN 0-8047-4482-3.
- Miller, George. 2000. Additional Views, 106th Congress Report: House of Representatives, 2d Session, 106-677, Graton Rancheria Restoration Act 
- Papina, Anne M. 2008. Nicasio (Arcadia Publishing, 2008).
- Futcher & Conover 1983:101; Papina 2008:7; Munro-Fraser 1880:289.
- Marin County's Original Ranchos
- Original Mexican Land Grants in Marin County
- Jack Mason, 1971, Early Marin, Petaluma: House of Printing, pp.70-76
- United States. District Court (California : Northern District)Land Case 404 ND
- Hoover 2002:190.
- Miller, 106th Congress Report
- Ogden Hoffman, 1862, Reports of Land Cases Determined in the United States District Court for the Northern District of California, Numa Hubert, San Francisco
- United States. District Court (California : Northern District)Land Case 392 ND
- Report of the Surveyor General 1844 - 1886
- Olompali Park Filled With History, Reutinger, Joan. The Coastal Post, Sept. 1997
- The Settlement of Nicasio: James Black