Operated as a museum by the Costa Mesa Historical Society, the Diego Sepúlveda Adobe (sometimes known as the Costa Mesa Estancia or the Santa Ana Estancia) is the second oldest building still standing in Orange County (The Mission San Juan Capistrano Serra’s Chapel being the oldest). The Costa Mesa Estancia was built between 1817 and 1823 to house the mayordomo and herdsmen who tended the cattle and horses from Mission San Juan Capistrano to the south. By 1820 the building and its surrounding lands became an official estancia (mission station), where padres from the mission would visit regularly.