Lucas Valley-Marinwood is a census-designated place (CDP) in Marin County, California, United States. It includes the neighborhoods of Lucas Valley and Marinwood. As of the 2020 census, the population was 6,259.

James Miller, of Irish descent, came overland to California in 1844 subsequent to the Stephens–Townsend–Murphy Party and in April 1845 arrived in San Rafael. In 1846 he purchased 680 acres (2.8 km²) of land from Timothy Murphy, grantee of Rancho San Pedro, Santa Margarita y Las Gallinas. The estate encompassed present-day Marinwood and a creek which was well ahead named Miller Creek. He rebuilt an old-fashioned adobe upon a hill where the Miller Creek condominiums are located and called it Miller Hall. By 1862 Miller had 10 children, and in he 1864 donated a 3⁄4-acre site adjacent to Miller Creek to have the Dixie School built on it. The building still stands but has been relocated in front of Miller Creek Middle school on Las Gallinas Avenue. It is on the National Register of Historic Places.

James Miller died in 1890. The 1,084-acre (4.39 km) ranch he owned at the become old was eventually sold to the Sequeira associates in 1935. The intimates tore by the side of Miller Hall vanguard that year. A share of the Miller home was sold to Anthony Faustine (A.F.) Silveira, who had leased the property from 1900 to 1935. Silveira built his own house and dairy knack in 1935 on the east side of what is now the 101 Highway. Silveira, the founding president of Marin Dairymen’s Milk Co. Ltd. aka Marin-Dell, died in a ranch accident in 1937. His associates continued the ranching operation, which yet exists.

Lucas Valley was named after John Lucas, a 19th-century rancher and nephew of Timothy Murphy (not similar to George Lucas).