Halcyon /ˈhælsiən/ is an unincorporated community of about 125 acres (50 ha) in San Luis Obispo County, California, United States, just south of Arroyo Grande.

The Temple of the People was founded in Syracuse, New York, in 1898 by William Dower and Francia LaDue, members of the Esoteric Section of the Theosophical Society.

Dower, who was a medical doctor, and LaDue founded the Halcyon Hotel and Sanatorium, where all manner of addiction and nervous ailments as well as tuberculosis were treated and which remained open until 1949.

The Blue Star Memorial Temple building, designed by architect Theodore Eisen of Los Angeles, was constructed in 1923 and named in honor of LaDue.

Cethil Mallory, member and building contractor, worked on many of the single-family homes in Halcyon with the help of his three sons, John, David, and Roland.