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.