Santa Ysabel is an unincorporated community in the Santa Ysabel Valley of eastern San Diego County, in southern California.
The 1818 Santa Ysabel Asistencia is located here, a Spanish mission asistencia (sub-mission) of Mission San Diego de Alcalá. The town site is within the former Rancho Santa Ysabel, an 1844 Mexican land grant to José Joaquín Ortega and Eduardo Stokes. In 1878, what began as the town of Santa Ysabel began with a store owned by C. R. Wellington, and grew to include a hotel and a blacksmith. By June 26, 1889 it had acquired its own post office.