Diego Sepúlveda Adobe, Adobe home in Costa Mesa, California.

The Diego Sepúlveda Adobe is an earthen-brick house in Costa Mesa, California, built with thick adobe walls and wooden beams in the Spanish colonial style. The building sits close to the Santa Ana River bed and is among the oldest surviving homes in this part of the state.

The house was built between 1817 and 1823 as a residence for the mayordomo and herders of Mission San Juan Capistrano. These workers managed the cattle and horses that kept the mission's ranching operations running.

The adobe now holds a local history museum run by the Costa Mesa Historical Society. Its name recalls Diego Sepúlveda, a former alcalde of Mexican-era Los Angeles who received the building and surrounding land from the U.S. government around 1868. The site is also known as the Costa Mesa Estancia or Santa Ana Estancia, from its years as a mission station.

The adobe now serves as a local history museum run by the Costa Mesa Historical Society, so visiting arrangements go through that group rather than a public park service. It stands on the banks of the Santa Ana River, roughly six Spanish leagues north of Mission San Juan Capistrano, the mission whose herdsmen it once housed.

The adobe served as a lookout post when the French privateer Hippolyte de Bouchard attacked Mission San Juan Capistrano on December 14, 1818. From its position above the Santa Ana River, the station overlooked both the cattle grazing lands and the Tongva village of Lupukngna.